THE POPULAR SCIENCE MONTHLY.
city on the list is Sioux City, Iowa, and the next is Duluth, Minn., the expense being in the first $23.91 and in the second $23.08; but this great expense is probably due to the extensive construction of streets in a recent period, and therefore the expense of these two cities should not be compared with that of others. Throwing out the cities with abnormal conditions, it is probable that San Francisco is the highest cost city in the list of fifty given in the table, the expense being $11.41 per capita.
The table will be found interesting in many respects, as comparisons can easily be made for one city with another, not only as to total per capita cost, but as to the items enumerated. Looking at the city of New York, for instance, the table means that it would cost a family of five $35.25 per annum for the benefits accruing to it from the use of streets and the cleaning thereof, for public lighting, for the maintenance and repairs of sewers, for police protection, for the protection of the fire department, and for the use of water. No one can object to an expense for a family of five persons no higher than that named for all these great advantages. The working-man with five in his family is not taxed this $35.25 directly, as intimated, but he has to pay it in rent and the cost of his living. Is it an unreasonable addition to his annual expenses? is the question. It does not matter whether the total expense is high or low for all the advantages detailed; the great question is. Could they be furnished as efficiently and as well in every respect for a less sum, with the integrity of all departments preserved? If they could, then a man is entitled to the less expense. If not, he should certainly be entirely satisfied with the great return which he now gets for the money expended.
By CASEY A. WOOD, C. M., M. D.,
INSTRUCTOR IN OPHTHALMOLOGY, CHICAGO POST-GRADUATE MEDICAL SCHOOL.
OUR train has been traveling for the past twenty-four hours over that part of a transatlantic route which stretches from the Sierra Madre to the extreme borders of the great Mohave Desert. There are many interesting things to be seen along this line of travel, but nothing more striking than the curious optical phenomena presented by the pleasing alternation of vast plain with rugged mountain. For example, not far from the last station we come upon a lofty peak overtopping the surrounding hills. It seemed to be about ten miles away, but was in reality fifty.
As is well known to the student of optics, the apparent size of an object is mainly dependent upon the size of the image which