7 16 



THE POPULAR SCIENCE MONTHLY. 



that the winds and condition of the north- 

 ern hemisphere have any perceptible influ- 

 ence at the equator, and ascribes the mild- 

 ness and uniformity of the equatorial tem- 

 perature to the prevalence of the rainy sea- 

 son in our winter, the southern summer 

 months. Water acts during this season to 

 reduce the temperature through its great 

 capacity for heat, through the screen of 

 clouds which it interposes between the sun 

 and the surface of the earth, and through 

 evaporation, and this upon the higher as 

 well as upon the lower strata of air. It is 

 admitted that winds have some effect as 

 aids to the cooling, but the insignificance 

 of their influence, as against any active 

 heat-producing force, and in the absence of 

 moisture, is shown by the fact that the 

 Sahara is the hottest region in the world, 

 notwithstanding the winds that blow over 

 it from the cool Mediterranean. 



Messages by Heliograph. The usefulness 

 of the heliograph was recently satisfactorily 

 tested in the transmission of a dispatch from 

 General Stewart, in Afghanistan, announc- 

 ing the result of an attack on the British 

 troops, which was sent from Camp Ghuzni, 

 April 22d, and was received at the India 

 Office, London, on the following day. The 

 news could hardly have been brought more 

 speedily by electric telegraph. The helio- 

 graph, signaling right over the heads of 

 the enemy, if necessary, to stations which 

 may be few and far between, does not re- 

 quire any route to be kept open, and can not 

 be interrupted. A ten-inch mirror, that be- 

 ing the size of the ordinary field-heliograph, 

 is capable of reflecting the sun's rays in the 

 form of a bright spot to a distance of fifty 

 miles, where the signal can be seen without 

 the aid of a glass. The adjustment of the 

 instrument is very simple. If an army 

 corps, having left its base where a heliograph 

 station is established, desires to communicate 

 with the other division from a distance of 

 several miles, a hill is chosen and a sapper 

 goes upon it with his heliograph-stand con- 

 taining a mirror swung so as to move hori- 

 zontally and vertically. A little of the 

 quicksilver having been removed from be- 

 hind the center of the mirror, a clear spot 

 is made through which the sapper can look 

 from behind his instrument toward the sta- 



tion he desires to signal. Having sighted 

 the station by adjusting the mirror, he next 

 proceeds to set up in front of the heliograph 

 a rod on which is a movable stud, manip- 

 ulated like the foresight of a rifle. The 

 sapper, standing behind his instrument, di- 

 rects the adjustment of this stud until the 

 clear spot in the mirror, the stud, and the 

 distant station are in a line. The helio- 

 graph is then ready to work, and the sap- 

 per has only to take care that his mirror 

 reflects the sunshine on the stud just in front 

 of him to be able to flash signals so that they 

 may be seen at a distance. 



Ocean Temperatnres in the Pacific and 

 Atlantic. Herr von Boguslawski has been 

 led, from a comparison of the results of re- 

 cent deep-sea investigations, to the following 

 conclusions respecting the temperatures of 

 the Atlantic and Pacific Oceans: 1. The 

 water of the North Pacific is, in its whole 

 mass, colder than that of the North At- 

 lantic. 2. The water of the South Pacific 

 is, down to 1,300 metres (4,225 feet), some- 

 what warmer than that of the South At- 

 lantic, but below this depth colder. 3. The 

 bottom temperatures are generally lower in 

 the Pacific than in the Atlantic at the same 

 depths and in the same degree of latitude ; 

 but nowhere in the Pacific are found such 

 low bottom temperatures as in the Antarc- 

 tic portion of the South Atlantic, between 

 36 and 38 south and 48 and 33 west lon- 

 gitude, in which bottom temperatures of 

 - 3 C. to - 6 C. have been measured. 

 4. In the western parts of the Pacific, 

 and the adjoining parts of the East Indian 

 Archipelago, the temperature of the water 

 reaches its minimum at depths beween 

 550 and 2,750 metres (1,787 and 8,937 

 feet), remaining the same from this depth 

 to the bottom. In the whole of the At- 

 lantic the temperature from 2,750 metres 

 (8,937 feet) to the bottom gradually though 

 very slowly decreases. 



The Harvard Medical Course. Profes- 

 sor James C. White, of the Medical School of 

 Harvard University, states that the enlarge- 

 ment of the course of instruction which was 

 adopted by the department ten years ago 

 has been followed by a general elevation of 

 the standard of medical education through- 



