Page:Popular Science Monthly Volume 23.djvu/423

Rh and transformed into a respectable body of water. These and other hygienic improvements which have followed in the wake of the fault-finder will doubtless render Ocean Grove and its close neighbor, Asbury Park, satisfactory places for visitors during the season of 1883. That the past winter's work is likely to prove efficient may be gathered from Mr. Stokes's letter, in which he says, "The State Board of Health reports that the sanitary matters of the Grove progress satisfactorily."

It is hoped that the pleasure with which this account is given of a better sanitary prospect for the present summer over that of former years will prove previous charges of improper drainage to have been made only in that spirit which sounds an alarm to prevent danger.

Messrs. Editors:

an article in the June number of your magazine, entitled "Cost of Life," there are some mathematical calculations, or rather blunders, that make one wonder how they could have been put forth in any journal, though making less claims to science than your valuable magazine. It is gravely stated that a man weighing 150 pounds upon the earth would, upon the planet Jupiter (having 300 times the earth's mass), weigh 45,000 pounds $$=$$ 224$1⁄2$ tons. The relative mass of Mars is said to be $1⁄60$ that of the earth, and, therefore, the man spoken of above would weigh only 2$1⁄2$ pounds upon Mars. Now, if the law of attraction as first announced by Newton, and now taught to every schoolboy, is correct, the weight of the above man upon Jupiter would be 2∙55 (two and $55⁄100$) times his weight upon the earth $$=$$ 382$1⁄2$ pounds—enough to make him decidedly uncomfortable, but still not quite 22$1⁄2$ tons. In regard to Mars there are two errors: first, his mass is $11⁄100$ that of the earth, not $1⁄60$ as stated; second, if it were $1⁄60$ it would not be right to divide 150 by 60, for that would disregard a very essential part of the great law or laws of gravitation. If the radius of Mars is ∙52 that of the earth, would not the supposed man weigh, if placed upon his surface, 61 pounds?

There may be some errors in these corrections, but I think they are trifling compared with those in Mr. Pratt's article.

Messrs. Editors:

me to call attention to certain assertions in the article headed "Cost of Life" in the June number of your journal. The points I speak of relate to gravity on the planets, and the statements made in regard thereto. It is declared that a man of 150 pounds weight would on Jupiter weigh about 45,000 pounds. It is an elementary truth in physics that gravity decreases as the square of the distance increases; wherefore, although Jupiter is more than 300 times as heavy as the earth, its diameter is more than eleven times that of the earth, and the relative weight must be divided by the square of the ratio. In this case the divisor is more than 121. The best determinations of the force of gravity on Jupiter give it at a little less than two and three fourths that on the earth. So the man of 150 pounds would, on Jupiter, weigh about 400 pounds, not that enormous figure quoted above.

So, gravity on Mars is more than half that on the earth, and our man would weigh 80 pounds, not 2$1⁄2$ as given in the article. Every similar statement in the whole course of the discussion is as badly in error as these here noticed.

It is well known that the destructive effect of a bullet fired by an explosive depends not on the power of gravity, but on that of the powder; and the philosophers who, on Mars, should attempt to catch bullets in their hands, might rue their philosophy. As science, the article harmonizes well with the kind in which Jules Verne is accustomed to indulge.



UR friend Dr. Dix Has deserted us. We have received divers sarcastic congratulations upon our new ecclesiastical alliance, implying that we had made no great acquisition, but we could not anticipate that we should be left in the lurch so soon. We were taken with the impressive declamation about the supremacy of the home sphere in the life of woman, and when Dr. Dix said, "These considerations give the turn to every thought of ours about woman's work"—and of course the preparation 