SCIENTIFIC.
331
Mr Paul Mays, of Switzerland, has lately printed a monograph on "Sustaining Bodies in Space by Motive Force." He says:
"The wings of a common fly vibrate at the rate of 430 strokes per second; those of the mosquito about 2000 times per second; therefore, according to the formulae which I have established, a number of common flies, weighing altogether 20 tons, and 130 tons of mosquitos require about one-horse power to sustain themselves in the air.
During the study of this question of sustaining forces in space, I came many times to what seemed to me a strange conclusion; for instance, that any piece of heavy metal must float on perfectly still water. But as it is impossible to have perfectly still water, the property is subordinate to certain conditions."
The absurdity of the first statement is apparent; for say, for instance, that it requires twice the exertion for a mosquito to rise at the rate of one foot per second than for him to remain stationary; then according to Mr. Mays, two-horse power would be sufficient to raise 130 tons at the rate of one foot per second. This is equivalent to 15,600,000 foot pounds per minute, or nearly 500 horse power.
His second statement may not be so absurd, but it is foolish nevertheless; for in any medium a heavier body will sink; even a leaden ball will sink through a rock after an infinite time, according to the theory of elasticity, which supposes that viscosity is a universal property of matter, the curve which represents the rapidity of change of form being tangent to the axis of force, and to the axis of time at infinite distances from the origin.
The greatest eastern elongation of Mercury will occur upon the 25th of this month, and the planet will be visible about ten days before and aftor this date. On
the 25th he sets about one hour and three quarters after the sun. Those who wish to behold this interesting planet will find the present an unusually favorable opportunity for the purpose. They should commence their search about three quarters of an hour after sunset, and first finding the familiar cluster of the Pleiades in the northwest, scan the sky a degree and three quarters south of the cluster, and a very slight distance west, when "The Sparkling One" will suddenly dart into view, shining with a peculiar luster on the glowing twilight sky.
—"Of what does color blindness consist,' is the oft repeated question since the tests by Profs. Bailey and Nichols are well under way.
According to Young's theory of color, there are three sets of nerves in the retina of the eye, each one sensitive in a certain degree to all wave lengths of light, but to one wave length in particular. The sensation of yellow. for instance, being caused by a wave length of light which affects the red and green nerves about equally, and the violet nerves only to a very limited extent. Thus we see that the sensation which we call yellow consists of a red and a green sensation principally. Now if a person were red color blind, that is if the red nerves were lacking, leaving only the green with a small amount of violet, and the and the person would class all yellow colors with green. But if he were green blind, he woulb class all yellow with red. In the first instance, if he were asked what color yellow was he would answer yellow, because he was taught to call it yellow, and because the word "yellow" conveys no real meaning in itself.
Color blindness is much more complicated than the above theory would seem to indicate, for it has to do with all varieties of shades and tints, and never in practice with pure colors such as are found in the spectrum.