As this dry cold air underruns the moist warm air at the earth's surface, or as two areas of high pressure flowing toward each other must lift up the lighter air between them and set it into cyclonic rotation, we must, therefore, recognize the general conclusion that Espy's aspiration cyclone as developed by Ferrel is not the only form of cyclone, but that those due to descending cold air, and, therefore, having the general circulation of the atmosphere as their fundamental cause, are equally entitled to consideration. To this last and latest development from the theoretical side, I need only add that the study of the motions of the clouds has enabled me to assert that there is no form of motion known to the student of mechanics of fluids but what is to be found beautifully illustrated in some important phenomena of the atmosphere. The experiments on the motions of water and of air, and the measurements thereon that you may make in a well-appointed physical laboratory, are repeated by Nature on a large scale in the atmosphere."
Antiquity of the Wheelbarrow.—The invention of the wheelbarrow has been generally ascribed to Blaise Pascal, who lived about the middle of the sevententhcentury. M. Littre, in his Dictionary, attributes it to one Sieur Dupin, in 1669, seven years after Pascal's death. M. Gaston Tissandier, however, found in a copy of the Cosmography of Sebastian Munster, 1555, a curious woodcut representing a wheelbarrow pushed by a workman. Another plate in the same book shows a tramway wagon running on rails. Still earlier evidences of the existence of the wheelbarrow have been found by if. Bixio and M. F. Guerrero, who organized the retrospective exposition of the means of transportation, which was held at Paris in 1889. A manuscript history of the sangreal of the thirteenth century contains' a picture of one man shoving another in a wheelbarrow of a style now in general use. A manuscript—Vita et Passio S. Dionysii Areopagi—of the fourteenth century, has a representation of a wheelbarrow of another model, which is used in carrying a bundle. A very artistic picture in a manuscript—La Vie et les Miracles de Notre Dame—of the fourteenth century, represents a hospital where Sisters are taking care of wounded, lame, deformed, or paralytic persons, to which a man is wheeling a new patient. A miniature in an illustrated edition of Quintus Curtius, of the fourteenth century, shows a workman wheeling building material, who is assisted in sustaining his load by a strap over his shoulders. These evidences testify to the use of the wheelbarrow as early as the thirteenth century, and it may have been an old invention then.
Trees and Extreme Temperatures.—The power of trees, says a note in Garden and Forest, to regulate their own temperature to a certain extent is seen in the fact that their twigs are not frozen through in winter; nor does their temperature increase in summer in proportion to the temperature of the surrounding atmosphere. The bark is a bad conductor of heat, and is to a certain extent the clothing in which the plant is wrapped. The surface evaporation of the leaves produces in summer a freshness in them that causes them to feel cool even on hot days. Evaporation, however, does not explain the coolness of many kinds of fruit that are inclosed in a hard envelope, through which it seems almost impossible. Hooker mentions a fruit grown by the Ganges in a soil having a temperature of from 90° to 104°, the temperature of the juice of which had only 72° Fahr.
Liquid Air and Liquid Oxygen.—A lecture was recently delivered at the Royal Institution, London, by Prof. Dewar, embodying the results of his recent investigations into the properties of matter at excessively low temperatures, and in particular of oxygen and atmospheric air in the liquid condition. The lecture was illustrated by experiments such as have never before been attempted in a lecture-room. Liquid oxygen was produced in the presence of the audience literally by pints, and liquid air was handed round in claret glasses. While oxygen boils in air at 182° C. below zero, the researches of Lord Kelvin and Prof. Tait indicate that temperatures below -274° C. will not suspend all the activities of matter. As this is far below even the calculated boiling-point of liquid hydrogen, the absolute zero seems to recede as we advance. The purely chemical rela-
