July 6, 1888.] 



SCIENCE. 



be used, too, on larger yaclils, and for pleasure-boats by those who 

 can afford them, and where there are facilities for reacliing the 

 battery. An important use just at present is to call attention to the 

 possibilities of storage-batteries, and to encourage inventors to im- 

 prove the present uneconomical and weighty types. 



The launch in question is twenty-eight feet long, has six feet 

 beam and a depth of three feet. 'I'he batteries are under a couple 

 of Ijenches running fore and aft. The motors are under the deck 

 aft. The motors are governed by a handle near the steering-wheel. 

 With seven-horse power the boat is said to make twelve miles, 

 with two-horse power about si.\ miles, an hour. 



Cost of Electric Traction. — The following table is the re- 

 sult of calculations made by experts on the cost of horses, cables, 

 and electric storage-cars on the Fourth Avenue street-car line. 

 New York : — 



Electric. Horse. Cable. 



•Costolcars i .54 .81 



Motive pouor i 1.45 1.06 



Constriicticn of roadway I .53 2.09 



Depreciation and repairs i 1.47 2.04 



Operating expenses (including wages). i 3.3S 1.71 



Total 5 7.37 7.71 



Average i 1.47 1.55 



For this road, then, storage-cars would, provided the estimate be cor- 

 rect, be much cheaper than any other system. Fortunately, these fig- 

 ures will have a practical test, since the Julien Company is equipping 

 ten storage-cars for the line. So much for storage-cars. Where 

 overhead wires are permissible, there seems no doubt of the ad- 

 vantages of electric traction. The Union Passenger Railway in 

 Richmond, with the Sprague system, is carrying over 250,000 

 passengers a month, at a cost of less than 1+ cents a car-mile ; 

 the total operating expenses, every thing included, being only 47 

 per cent of the receipts. What electric railway systems using a 

 conduit between the tracks for their conductor can do, remains to 

 be seen. For haulage in mines, the reports are most encouraging. 

 Mr. Shaefer, at a meeting of the Engineers' Club of Philadelphia, 

 stated that the cost per ton-mile in the anthracite-coal mines was as 

 follows : mules, 1.82 cents ; steam, .6 cent ; electric motors, ,4 to .67 

 cent. Considering the very obvious advantages of electricity as 

 compared with steam in mining-work, the figures are strongly in 

 favor of electricity for traction in mines. Outside of cost, elec- 

 tricity presents the advantages of cleanliness and perfect control ; 

 and the above figures, taken in two cases from actual and continued 

 experience, show, that, when properly applied, it is superior in econ- 

 omy as well. 



Lightning-Flashes. — W. Kohlrausch has estimated the cur- 

 rent and quantity of electricity in a lightning-flash. He calculates 

 that it will take 9,200 amperes 10 melt a copper rod of 2.5 centi- 

 metres diameter. Such a current concentrated in a flash would 

 contain from 52 to 270 coulombs, which would decompose from 5 

 to 25 milligrams of water, and form 9 to 45 cubic centimetres of 

 explosive gas. If this energy were stored up and distributed for 

 electric-lighting, it would require from 7 to 35 flashes to keep one 

 incandescent lamp lighted lor an hour. 



An Electro-Chemical Radiophone. — The London Ekc- 

 Irician gives an abstract of a communication to the Acadernie des 

 Sciences by MM. Chaperon and Mercadier, describing a galvanic 

 cell made by them which is sensitive to the action of light. " It 

 consists of a plate of bright silver covered by the electrolysis of 

 sulphate of sodium with a thin layer of sulphide of silver, immersed 

 in some electrolyte other than an alkaline sulphide, water contain- 

 ing a trace of sulphuric acid being as good as any thing. The 

 electro-motive force is feeble and variable, and the cell polarizes 

 rapidly, but its current undergoes an instantaneous change when 

 exposed to daylight or even to weak artificial light. The authors 

 investigated the rapidity of action by exposing the cell to the beam 

 of the oxyhydrogen light, made intermittent by passing through a 

 revolving wheel pierced with holes. A telephone was included in 

 the battery circuit, and sounds were produced so high in the scale 

 as to correspond to iTiore than 1,000 vibrations a second, which 

 showed that the electro-chemical effect must be produced in less 

 than ^s'su of a second, No corresponding change was produced 



in the resistance of the cell : so the effect of the light must be to 

 cause a variation in the electro-motive force. 



Experiments on the Electric Arc. —The fall of potential 

 in the electric arc has been generally held to be due to two causes, 

 — a resistance increasing with the length of the arc, and a counter 

 electro-motive force independent of the length. This may be ex- 

 pressed by the formula /?= a-^bl, where a and b are constants, 

 and / is the length of the arc. Dr. Lecher, in a paper in the dn- 

 trnlblatt filr Elcctrolcchnilc, describes experiments which tend to 

 disprove this view. He first found that the resistance of the arc 

 does not increase very rapidly when it is extinguished : this he 

 showed by putting the primary of an induction-coil in the arc-lamp 

 circuit, first pulling the carbons apart, and second extinguishing 

 the lamp. There was a spark in the secondary in the first case, but 

 not in the second : so the resistance, on extinction, could not have in- 

 creased with very great rapidity. This being the case. Dr. Lecher 

 placed in the lamp-circuit a galvanometer, the needle held against a 

 stop tor the direct current, but free to swing in the opposite direction. 

 He then suddenly cut out the feeding-current, and there was no 

 swing of the galvanometer-needle in the opposite direction : so, if 

 there was a counter electro-motive force in the arc, it must have 

 disappeared at the same time the feeding-current ceased. To see 

 if the difference of potential of the arc depends on the temperature 

 of the carbons, they were heated by a blowpipe. With a normal 

 difference of 42 volts, this rose to 48 volts when the positive, and 

 52 volts when the negative, carbon was heated. When the carbons 

 are horizontal, the potential difference is less than when they are 

 vertical, on account of the higher temperature in the latter case. 

 When the carbons are cooled, the potential difference is less. For 

 example, representing the difference by a-\-bl. 



Carbons horizontal, uncooled 33 



" horizontal, cooled 25 



4.5' ±'-3 volts. 



5.0/ ±3.0 " 



To find in what part of the arc the fall of potential really occurred, 

 a carbon rod of small diameter was introduced into the arc, and 

 the difference of potential between it and the carbon electrodes was 

 taken. It was found that the difference of potential between the 

 -I- carbon and aiiy part of the arc was about 36 volts. This being 

 the case, it is assumed that the rest of the fall of potential is at the 

 —carbon. Dr. Lecher also experimented on the nature of the cur- 

 rent forming the arc, but the method used is questionable. He 

 claims that his investigations show : i. The existence of a back 

 electro-motive force is doubtful ; 2. The difference of potential is 

 affected by temperature ; 3. If the negative electrode is platinum or 

 iron, the discharge is discontinuous. 



The Radio-Microphone. — Mr. C. Vernon Boys has de- 

 scribed before the Royal Society an instrument for measuring very 

 small changes of temperature. "It is an extremely delicate form of 

 thermopile, consisting of a square frame made of one turn of one 

 square centimetre, of which three sides are thin copper wire, and 

 the fourth is a compound bar of antimony and bismuth, each piece 

 being 5x5x1 mm., soldered edge to edge. This frame is sup- 

 ported by a thin rod to which is fastened a mirror, and the whole is 

 hung by a tortion fibre in the field of a powerful magnet. When 

 radient energy falls on the centre of the compound bar, the frame 

 is deflected, and the amount of deflection measures the energ)-. 

 Adopting suitable dimensions, and using a very strong field, an in- 

 strument may be made capable of showing a change of tempera- 

 ture of the junction of one thousand-millionth of a degree." 



BOOK-REVIEWS. 

 Forms of Animal Lift: a Manual of Comparative Aiuxtomy. By 

 George Rolleston. 2d ed., revised by W. Hatchett Jack- 

 son. Oxford, Clarendon Pr. 8". (New York, Macmillan, 

 S9-) 

 Those who in years past have been familiar with Rolleston 's 

 ' Forms of Animal Life ' will welcome the very much enlarged and 

 modernized edition that makes its appearance after a lapse of sev- 

 enteen years. Opinions may and will differ as to how the princi- 

 ples of comparative anatomy are best taught, but no one \s'ill deny 



