Popular Science Monthly/Volume 52/November 1897/Fragments of Science
Birds and Farm Pests.—Mr. F. E. L. Beal, in a paper on Some Common Birds in their Relation to Agriculture, observes that whether a bird is injurious or beneficial depends almost entirely on what it eats. If crows or blackbirds are seen in numbers about cornfields, or if woodpeckers are noticed at work in an orchard, it is perhaps not surprising that they are accused of doing harm. Careful investigation, however, often shows that they are actually destroying noxious insects, and also that even those which do harm at one season may compensate for it by eating noxious species at another. Insects are eaten at all times by the majority of land birds, and during the breeding season most kinds subsist largely and rear their young exclusively on this food. When insects are unusually plentiful they are eaten by many birds which ordinarily do not touch them. Within certain limits birds feed upon the kind of food that is most accessible. Thus, as a rule, insectivorous birds eat the insects that are most easily obtained, provided they do not have some peculiarly disagreeable property. It is not probable that a bird habitually passes by one kind of insect to look for another that is more appetizing, and there seems little evidence in support of the theory that the selection of food is restricted to any particular species of insect, for it is evident that a bird eats those which by its own method of seeking are most easily obtained. Thus, a ground-feeding bird eats those it finds among the dead leaves and grass; a flycatcher captures entirely different kinds; and the woodpecker and warbler in the tree tops select still others. The practical value of birds in controlling insect pests should be more generally recognized. It may be an easy matter to exterminate the birds in an orchard or grain field, but it is an extremely difficult one to control the insect pests. It is certain, too, that the value of our native sparrows as weed destroyers is not appreciated. Weed seed forms an important item of the winter food of many of these birds, and it is impossible to estimate the immense numbers of noxious weeds which are thus annually destroyed. If birds are protected and encouraged to nest about the farm and garden, they will do their share in destroying noxious insects and weeds; and a few hours spent in putting up boxes for bluebirds, martins, and wrens will prove a good investment.
Kites and Balloons in Meteorology.—The recent development of the kite for meteorological purposes, Mr. A. Lawrence Roche says in his paper on the subject, has taken place in the United States, while the use of automatic balloons for obtaining data at very great altitudes has hitherto been confined to Europe. Kites appear to have been first applied in meteorology by Alexander Wilson in Glasgow, who in 1749 raised thermometers attached to them into the clouds. Next was Franklin's electrical experiment. Between 1883 and 1885 E. D. Archibald made differential measurements of wind velocity by anemometers raised on kites fifteen hundred feet. In 1885 A. McAdie repeated Franklin's experiment on Blue Hill; and he afterward made other electrical experiments with kites. The invention of lightweight self-recording instruments made it possible to obtain graphic records in the air by means of kites; and the introduction of tailless kites by Mr. Eddy added to their usefulness. The thermograph raised by S. P. Ferguson, of Blue Hill, in August, 1894, was no doubt the first instrument recording continuously and graphically to be raised by kites; and it permitted simultaneous observations to be obtained in the free air and near the ground. This method of studying the meteorological conditions of the free air has ever since been in regular use at the Blue Hill Observatory. Probably the greatest elevation yet attained by kites, and certainly the highest level to which kites have lifted a meteorograph, is 8,740 feet above Blue Hill. This was accomplished October 8, 1896, by the aid of nine kites, having a total area of 170 square feet, which gave a maximum pull at the ground of about a hundred pounds. The meteorograph remained during several hours higher than a mile, and good records of the indications of the barometer, thermometer, and hygrometer were brought down. More than one hundred records of atmospheric pressure, temperature, and relative humidity of the air, or wind velocity at intermediate heights up to the extreme altitude mentioned have been obtained. Kites furnish a ready and accurate method of measuring the heights of certain low and uniform clouds. Changes of wind direction in the different air strata are determined from the azimuths of the kites. To reach much higher altitudes than three miles unmanned free balloons have been considerably used in France and Germany. These balloons, which carry self-recording apparatus, rise until equilibrium is attained in the rarefied air, when they lose their buoyancy and fall to the earth. Most of them have been recovered, with the instruments and records uninjured.
The Education of an Engineer.—Criticising the present methods of education, especially for qualifying students in mechanical science, Mr. G. F. Deacon asked, in his British Association sectional address, "Are we not in some cases attempting, at too early a stage, the teaching of subjects instead of principles? I mean including the practical working of details which will become the regular work of the student in the office or works of an engineer. . . . I do not say that subject training of this kind at college may not be useful; but we have to consider whether it does not, for the sake of some little anticipation of his office work, divert the attention of the student from the better mastery of those principles which it is so essential for him to grasp at the earliest possible time, and which do not limit his choice in the battle of life to any branch whatever of the profession or business of an engineer, but which, on the contrary, qualify him better to pursue with success whatever branches his inclination or his opportunities or his means may suggest." The author pointed out as a danger in the usual limitations of compulsory subjects for examinations for certificates and degrees, that in view of them subjects not made compulsory may be neglected, however important to the engineer they may be; and he recommends that a certain very moderate standard in all such subjects should be made compulsory if a certificate of proficiency is to be given in engineering or physical science.
History of Color Photography.—In a recent lecture before the Oxford University Junior Scientific Club, Captain W. de W. Abney gave a very good account of the present state and history of color photography. The first process described was that based on the three-color negatives—three negatives being taken, one through an orange, one through a green, and one through a blue screen. These negatives are developed in the ordinary way, and then viewed through three superposed color screens corresponding with those through which the negatives were taken. This process produces very beautiful results, but is obviously limited in application and is not true color photography. The next process described was that of Dr. Joly, of Dublin, who, basing his work on the same theory of color vision as the preceding, reproduces in color by means of a single negative. The human eye is incapable of separating points or lines which lie very close to one another. Dr. Joly's method utilizes this fact by ruling on a transparent screen lines only one two-hundredth of an inch broad, and very close together, and coloring them alternately red, green, and blue. The negative is taken through this screen, and then developed and viewed through a similarly colored screen, when the picture appears in approximately its natural colors. The viewing differ from the taking screens in both of these processes. The taking screens must not be such as to allow only monochromatic light to pass, but must allow a certain amount of overlapping. The viewing, on the contrary, are made as monochromatic as possible. Instead of using transparencies and colored films, transparent inks may be used to produce pictures by three printings. The oldest process described is that of the production of color by the action of light itself, or the true color photography. Somewhere about 1847 Becquerel found that if, instead of iodizing a plate, he chlorinized it and then exposed it to white light, it gradually assumed a violet tint; and if in this state he exposed it to the spectrum, he was able to obtain the colors of the spectrum on it. Unfortunately, however, these colors were not permanent, and no method has been devised for fixing them. The last method described by Captain Abney was that of Lippmann, who found that if by means of reflection he obtained stationary waves in the film, on development the silver was deposited between the nodes. On reflecting light from such a "noded" plate the proper light alone was reflected, and the photograph, viewed at a particular angle, appeared in its natural colors. If looked at by transmitted light these photographs have merely the appearance of ordinary transparencies. This method is known as the interference method, because the stationary waves which produce the nodes on the plate are caused by the interference of the normal light vibrations.
Distribution of Species by Man.—The Spread of Species by the Agency of Man was the subject of Chairman L. O. Howard's address before the Botanical Section of the American Association. The author showed that while natural spread had been the rule for centuries, the agency of man has become preponderating with the improvement of commercial intercourse between nations. In the intentional introduction of useful plants and flowering plants from foreign countries species sometimes escape from cultivation and become weeds. The intentional introduction of wild animals has generally been disastrous, as those of the mongoose in Jamaica and Australian flying foxes in California. Accidental introductions have been more powerful in extending the range of species and in changing the character of the plants and animals of a given region than intentional introductions. The era of accidental importations began with the beginning of commerce, and has grown with the growth of commerce. The vast extensions of international trade of recent years, every improvement in rapidity of travel and in safety of carriage of goods of all kinds have increased the opportunities of additional introductions, until at the present time there is hardly a civilized country which has not firmly established and flourishing within its territory hundreds of species of animals and plants of foreign origin, the time and means of introduction of many of which can not be exactly traced, while of others even the original home can not be ascertained. The paper closed with a suggestion that much may be accomplished by wisely planned and guarded introductions, as in the case of the Australian ladybirds introduced into California and the Sandwich Islands through Albert Kaebele.
Fields for Exploration in South America.—Mr. J. Scott Keltie showed in his geographical address at the British Association that there is a wider and richer field for exploration in South America than in any other continent—even than in central Africa. Along the great river courses our knowledge is fairly satisfactory, but the immense areas, often densely clad with forests, lying between the rivers, are almost unknown. In Patagonia, a great deal has recently been done by the Argentine Government; still, in the country between Punta Arenas and the Rio Negro we have much to learn; while on the west coast range, with its innumerable fiordlike inlets, its islands, and peninsulas, there is a fine field for the geologist and the physical geographer. Indeed, throughout the whole range of the southern Andes, systematic exploration is wanted. There is an enormous area lying to the east of the northern Andes, and comprehending their eastern slopes, embracing the eastern half of Ecuador and Colombia, southern Venezuela, and much of the country lying between that and northern Venezuela, including many of the upper tributaries of the Amazon and Orinoco, of which our knowledge is of the scantiest. Even the country lying between the Rio Negro and the Atlantic is but little known. There are other great areas, in Brazil and in the northern Chaco, which have been only partially described. A survey and detailed geographical and topographical description of the whole basin of Lake Titicaca is a desideratum.
Screw Propellers and Cavitation.—In a paper recently read at the International Congress of Naval Architects and Marine Engineers, by Mr. S. W. Barnaby, we find some interesting data on the above subject. Several years ago the author, in conjunction with Mr. Thornycroft, observed and described this phenomenon of cavitation at high speeds, and suggested that the speed of vessels was approaching a point at which propulsion by screws would become less efficient. If a cavity be formed in any manner in the interior of a mass of water it will tend to become filled with water vapor and with any air which may be in solution, since ebullition takes place at ordinary temperatures in a vacuum. The method used thus far for overcoming this tendency is an increase of propeller-blade surface; in one instance, by increasing the surface forty-five per cent without materially changing the diameter or pitch of the propeller, the same speed (twenty-four knots) was obtained with six hundred and fifty less horse power, and with a decrease of slip to seventeen and a half per cent instead of thirty per cent. The number of revolutions required for twenty-four knots with the screws of small area sufficed to drive the vessel at 28·4 knots when the blade area was increased. The vibration was extreme and dangerous with the narrow blades, but was of a quite normal and unimportant character when the blades were widened. Mr. Barnaby thinks that cavitation will be a source of much trouble in the future. Already it is becoming difficult to obtain the requisite area in screws of "destroyers" without either resorting to an abnormal width of blade or to a larger diameter and pitch ratio than would otherwise be preferable. The one expedient gives undue surface friction, and the other necessitates a reduction in the rate of revolution, and therefore a heavier engine.
Pure and Commercial Science.—It should hardly need saying, as Prof. H. Marshall Ward observes in his British Association sectional address, that the fact that a scientific discovery is found to have a commercial value is no argument against the scientific value of the research; yet some are disposed to depreciate research that may advance economical ends. There are in agriculture, forestry, and commerce generally, Prof. Ward continues, "innumerable and important questions for solution, the investigation of which will need all the powers of careful observation and industrious recording of which a scientific man is capable. But while I emphatically regard these and similar problems as worthy the attention of botanists, and recognize frankly their commercial importance, I want carefully and distinctly to warn all my hearers against supposing that their solution should be attempted simply because they have a commercial value. It is because they are so full of promise as scientific problems that I think it no valid argument against their importance to theoretical science that they have been suggested in practice. In all these matters it seems to me we should recognize that practical men are doing us a service in setting questions, because they set them definitely. In the attempt to solve these problems we may be sure science will gain, and if commerce gains also, so much the better for commerce and indefinitely for us. But that is not the same thing as directly interesting ourselves in the commercial value of the answer. This is not our function, and our advice and researches are more valuable to commerce the less we are concerned with it."
Some New Facts regarding Yeast.—Some interesting experiments have been under way during the past few years regarding the phenomena of fermentation. It has been generally thought that the alcoholic fermentation of sugar by yeast differs from the ordinary hydrolytic processes of the enzymes in that the actual presence of the living yeast cell was an essential. Some investigators have doubted this, however, and have thought that alcoholic fermentation was simply an example of ordinary enzyme action of special complexity. These views were partially supported by some experiments of Dr. E. Buchner, announced in the early spring; and it is now reported that later experiments from the same laboratory still further confirm this view, and, in fact, make it almost a certainty. Dr. Buchner, by pounding up pure yeast with quartz sand and adding a certain amount of water, was able to squeeze out under a pressure of from four hundred to five hundred atmospheres a liquid which, after thorough filtering, was of an opalescent appearance and possessed an agreeable yeastlike odor. All care was taken to exclude any organism from the liquid, and it was found that under these conditions it was able to excite alcoholic fermentation in solutions of suitable sugars. The addition of chloroform, even up to the saturation point, does not inhibit the fermentative process, and this, in conjunction with the fact that the activity of the solution is not affected by the presence of the ordinary antiseptie substances, and that the solid residue, after evaporation at low temperatures, is found to yield an active solution even after being kept for two or three weeks, seems to show conclusively that the fermentation in these cases is not brought about by living protoplasm in any form, but is really due to an enzyme ferment which the author calls zymase. This is further confirmed by the fact that dried yeast heated to 100° for six hours, while incapable of further development, still yields an active solution when treated with a sterilized thirty-seven-per-cent sugar solution.
Thirteen Years' Progress in Physiology.—The presidential address of Prof. Michael Foster in the Physiological Section of the British Association was devoted to a review of the progress of physiology during the thirteen years since the association previously met in Canada, and dealt largely in technicalities. The progress consists partly of the continuation of investigations previously begun, and of advance in investigations newly entered upon. An example of the former kind is the study of the mechanics of the circulation. The researches of Hürthle and Tigerstedt, of Roy and Adami, and others have left us wiser on this subject than before. So real, if not exciting, progress has been made with the problems of muscular contraction; we are some steps measurably nearer an understanding of what is the nature of the fundamental changes that bring about contraction, and what are the relations in the changes in the structure of muscular fiber. In respect to the beat of the heart, we have continued to approach nearer to the full light. Among other problems concerning which knowledge has advanced are those of the nature of secretion and of transudation, concerning which controversies have raged that have not been wholly unprofitable. Included in the new subjects of research are physiological chemistry in general, the nature and office of the secretions, the nervous system, and the workings of the brain—concerning which, "if increasing knowledge gives us increasing power so to mold a muscular fiber that it shall play to the best the part which it has to ply in life, the little knowledge we at present possess gives us at least as much confidence in a coming far greater power over the nerve cell."
The Tilting of the Lake Region.—The discussion of the geological history and future of the region of the Great Lakes was again brought up in the American Association by Dr. W. J. Spencer, who, after reviewing his investigations in former years of the ancient outlets of Lake Erie, spoke of the lake region as having been covered subsequently to the Glacial period by great bodies of water all at one level. One of these, Warren Gulf, which covered the lake basins, was broken up by the rise of the land, and Lakes Superior, Huron, and Michigan were formed, their water emptying to the northeastward and not into the Erie basin. Afterward the land rose higher to the northeastward, filled the rivers of the basins upward, and turned the upper lakes into Lake Erie. At the same time the rocky barriers caused Lake Erie to drown the western hundred miles of its basin, and the waters are now rising and will in a few centuries cover Toledo and Detroit. The evidence is recorded in the shore lines, which have been surveyed by Professor Gilbert, the author, and others. They have risen in some cases from four to seven feet per mile going northeastward in a period of about fifty years. Prof. G. K. Gilbert in another paper presented a comparison of surveys made on the lake shores twenty or more years ago and within the past year. It is found that changes have taken place, all of which show a rising of the land at the north or northeast as compared with the land at the south or southwest. The whole lake region appears to be undergoing a tilting toward the south southwest at such a rate that of two points a hundred miles apart, the northern rises five inches in a century as compared with the southern. The mean level of the lake rises at Chicago about an inch in ten years, or ten inches in a century. It is estimated that in about three thousand years all the overflow from the upper lakes will go to the Illinois. The Detroit and St. Clair Rivers will carry water from Lake Erie to Lake Huron instead of from Huron to Erie, and the Niagara River will run dry.
Canada's Oldest Geology.—The presidential address of Dr. D. M. Dawson before the Geological Section of the British Association comprised a comprehensive but highly technical account of the Pre Cambrian Rocks of Canada. At the close of his review the author said that the general tendency of our advance in knowledge appears to be in the direction of extending the range of the Palæozoic downward, whether under the old name Cambrian or under some other name applied to a new system defined, or likely to be defined, by a characteristic fauna. The somewhat arbitrary and artificial definition of the Olenellus zone as the base of the Cambrian seems to be not of world-wide application, and not even generally appropriate to North America; while as a base for the Palæozoic eon it is of still more doubtful value. In the Cambrian period as well as in much later geological times the American continent does not admit of treatment as a single province, but is to be regarded rather as a continental barrier between two great oceanic depressions, each more or less completely different and self-contained in conditions and history—that of the Atlantic and that of the Pacific. On the Atlantic side the Olenellus zone is a fairly well-marked base for the Cambrian; on that of the Pacific it is found naturally to succeed a great consecutive and conformable series of sediments, of which the more ancient fauna is now only beginning to be known.
The Thumb and Toes in Men and Apes.—The presidential address of Sir William Turner before the Anthropological Section of the British Association was devoted to some of the characteristics of human structure distinguishing it from that of the apes. Its language is largely technical. The description of the differences in the disposition of the thumb and of the toes presents many points of interest. Both in man and the ape the thumb is not tied to the index digit by an intermediate ligament, which, under the name of "transverse metacarpal," binds all the fingers together and restricts their separation from each other in the transverse plane of the hand. The great toe of the ape is similarly not tied to the second toe as the other toes are tied to one another and restrained in their movements. The hallux of the ape is therefore set free, and can, like the thumb, be thrown into opposition and be used as a prehensile digit. In the human foot the hallux is tied to the second toe by a continuation of the same transverse metatarsal ligament that ties the smaller toes together. Hence it is impossible to oppose the great toe to the surface of the sole in the way in which the thumb can be used, and the movements of the digits in the transverse plane of the foot are also greatly restricted. In the hand of both man and the ape the joint between the metacarpal bone of the thumb and the bone of the wrist is concavo-convex, or saddle-shaped, and permits of a considerable range of movements in certain directions, and notably of the movement of opposition. In the foot of man the joint is not thus shaped, and the range of movement is slight. One of the chief factors in the production of the movement of opposition is a special muscle, the opponents pollicis, which is so adjusted as to draw the entire digit over the surface of the palm. In the foot of the anthropoid apes there is not complete correspondence among the different species in the similar disposition for moving the great toe, and in some it is altogether absent, as it is in the foot of man.