3H 



SCIENCE. 



PERSONAL DANGER CONNECTED WITH 

 ELECTRIC LIGHTING. 



In a recent paper Mr. Swan, of Newcastle, says : 

 " While on the subject of alternating currents, I take 

 occasion to remark on a letter of Mr. Preece in the Times, 

 referring to the death of two persons, said to have occurred 

 through their taking hold of the wires in connection with 

 an apparatus supplying the current to Jablochkoff's candle. 

 One of these cases occurred some time ago ; the other was 

 more recent. Now, admitting for the moment that these 

 deaths occurred directly from the shock (which I consider 

 by no means proved), I do not think that the extreme 

 views put forth by Mr. Preece as to the dangers conse- 

 quent on electric lighting in general can be supported, 

 and for this reason : — The machine which supplies a 

 Jablochkoffs candle gives alternating currents ; the ma- 

 chines which supply the ordinary electric arc, which 

 supply my lamps, and which are more generally used for 

 lighting, give a current constant in one direction. Now, 

 although the physiological effect of the alternating cur- 

 rents is undoubtedly severe, yet the effect of touching the 

 wires from a direct-current machine is merely that you 

 feel at the moments of making and breaking contact a 

 slight shock, but while you have hold you feel almost 

 nothing. [Mr. Swan afterwards demonstrated practically 

 the harmlessness of the current by taking hold of the 

 wires from the dynamo-electric machine for some 

 minutes.] I think Mr. Preece, knowing how many real 

 difficulties are connected with electric lighting, should 

 hardly have added to these by magnifying to so great an 

 extent the dangers which in some cases may accompany 

 it." 



REPORT OF THE DREDGING CRUISE OF THE 



U. S. STEAMER BLAKE, COMMANDER 



BARTLETT, DURING THE SUMMER OF 



1880.* 



By Alexander Agassiz. 



The cruise was undertaken with the object of deter- 

 mining the exact relation of the fauna of the Atlantic 

 Ocean to that met with in the Gulf of Mexico, and in the 

 Caribbean Sea. In the Atlantic and Pacific oceans, deep- 

 sea soundings have generally been made to a depth of 

 1500 fathoms ; in the Gulf of Mexico, to a depth of 450 

 fathoms. Work was begun in June last, south of Cape 

 Hatteras, on a line parallel to the coast, and at an aver- 

 age distance of about 120 miles from it. 



Instead of finding a gently sloping sea-bed, as has 

 heretofore been supposed to exist in these latitudes, the 

 dredgers discovered, what proved to be, a continuation of 

 the plateau, of which the northern portion is known to 

 extend as far as Cape St. George, and of which the south- 

 easterly limit is supposed to rest on the Bahama Banks. 

 The western ledge on this plateau, was examined during 

 last summer's cruise, and proved very interesting from a 

 geological point of view. The eastern slope has not been 

 traced as yet. Its exact limits is a matter of conjecture, 

 but are to be determined in next year's cruise. The sides 

 of this plateau are steep. Three ship's lengths from a point 

 where a depth of 100 fathoms was reached, the sounding 

 apparatus did not strike bottom until 450 fathoms of the 

 line had been paid out. More animal life is found on the 

 edge of the plateau than elsewhere. The character of the 

 animals is, on the whole, the same as that of the species 

 found in the Gulf of Mexico and the Caribbean Sea. The 

 edges are composed of rich deposits of alluvia and mud, 

 washed from the top of the plateau by the action of the 

 Gulf stream, the course of which extends over the entire 

 length of this Atlantic plateau. The deposits of numer- 

 ous rivers flowing into the Atlantic Ocean serve to enrich 

 the western slope. These conditions are all favorable to 

 the preservation of animal life on the edges of this sub- 



* Read before the National Academy of Sciences, N, Y., 1880. 



marine highland, while on its top no animal life is to be 

 met with, a certain species of coral formation excepted. 

 Altogether the success, obtained by this expedition, was 

 great. The same set of officers has served for three 

 consecutive seasons. The same amount of work, which, 

 in the course of the first year's cruise, required three 

 months' time, during the past season has been accom- 

 plished in seven weeks. Work was continued day and 

 night. The rapidity with which the soundings were 

 made enabled eight dredges, each of them to the depth 

 of 800 fathoms, to be made every twenty-four hours. 

 Formerly, one deep-sea sounding was considered a good 

 day's work. 



<♦» 



THE DURATION OF THE ARCTIC WINTER.* 



By Leutenant F. Schwatka, U. S. N. 

 The generally received opinion, that the Arctic winter, 

 especially in the higher latitudes, is a long dreary one of 

 perfectly opaque darkness, is not strictly correct. In lat- 

 itude 83 20' 20" N., the highest point ever reached by 

 man, there are four hours and forty-two minutes of twi- 

 light on December 22, the shortest day in the year, in 

 the Northern Hemisphere. In latitude 82 27' N., the 

 highest point where white men have wintered, there are 

 six hours and two minutes in the shortest day, and it is 

 in latitude 84 32' N., 172 geographical miles nearer the 

 North Pole than Markham reached, and 328 geographi- 

 cal miles from that point, that the true Plutonic zone, or 

 that one in which there is no twilight whatsoever, even 

 upon the shortest day of the year, must be found. Of 

 course, about the beginning and ending of this twilight, 

 it is very feeble and easily extinguished by even the 

 slighest mists, but nevertheless it exists, and is quite ap- 

 preciable, on clear cold days, or nights, properly speak- 

 ing. The North Pole itself is only shrouded in perfect 

 blackness from November 13 to January 29, a period of 

 seventy-seven days. Supposing that the sun has set 

 (granted, the existence of a circum-polar sea, or body of 

 water, unlimited to vision) on September 24, not to rise 

 until March 18, for that particular point, giving a period 

 of about fifty days of uniformily varying twilight, the 

 Pole has about 188 days of continuous daylight, 100 days 

 of varying twilight, and J7 of perfect inky darkness 

 (save when the moon has a Northern declination) in the 

 period of a typical year. During the period of a little 

 over four days, the sun shines continuously on both the 

 North and South Poles at the same time, owing to re- 

 fraction parallax, semi-diameter and dip of the horizon. 



SIGSBEE'S GRAVITATING TRAP* 

 By Alexander Agassiz. 

 Lieutenant-Commander Sigsbee devised this trap to 

 ascertain the depth to which the animal fauna of the 

 ocean descends. The extisence of animal life at great 

 depths is extremely doubtful and this belief is confirmed 

 by the fact that, whether dredging in 50 or 2000 

 fathoms of water, there is always brought to the surface 

 the same species of animals. To secure water from 

 different depths, Lieutenant-Commander Sigsbee con- 

 structed cylinders with traps, which could he opened 

 from on board the vessel by lines, and which closed with 

 the pressure of the surrounding water as soon as filled. 

 They were found to sink 50 fathoms in 45 seconds. At 

 the depth of 50 fathoms the trap brought to the surface 

 the animals that usually float on the surface. At the 

 depth of from 50 to 100 fathoms the number of animals 

 decreased and only five species of pelagic forms were 

 found, while seventeen species had been discovered at 

 the former depth. Using every possible precaution the 

 apparatus was next sunk in from 100 to 150 fathoms of 

 water, but no animal life was found. The water was 

 perfectly clear. The dead bodies of pelagi require from 

 three to four days to sink in 1000 fathoms of water. 



+ Read before the National Academy of Sciences, N. Y., 1880. 



