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 supplyingthe 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 
Jablochkoff s 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- 
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 ot 
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 77 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 be 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., i88o r 
* Read before the National Academy of Sciences, N. Y., 1880. 
