ELECTRICITY. 



285 



municatea orders to the engineer. The poles 

 are numbered in mile -sections, from one to 

 twenty-six, and the miles are marked on the 

 poles as if milestones. By this means the en- 

 gineer, who keeps record of the condition of 

 the track, can report to the master-mechanic, 

 at the end of the trip, or sooner, any defect 

 within one hundred feet, by naming the num- 

 ber of the pole and section where work is 

 needed. The master-mechanic has charge of 

 maintenance of way, and, having reports by 

 telegraph, as above stated, he at once directs 

 where work is to be done." 



Improved Exciting Liquid. The American 

 Journal of Science, for April, contains an article 

 from Mr. S. B. Sharpies, recommending the 

 Bunsen cell substituting, however, for the 

 nitric acid the mixture herewith described, 

 which costs but little if any more than the 

 nitric acid alone, and is entirely free from 

 fumes : 



To prepare the exciting liquid, sulphuric acid of 

 1.84 sp. gr. is mixed with nine times its volume of 

 water and allowed to stand until the precipitated 

 lead has all settled. The clear acid is then decanted 

 and is fit for use. This plan of preparing the acid 

 has been in use in this laboratory for some years, 

 and gives very good results, local action being^ almost 

 entirely prevented by the removal of the lead. 



To prepare the absorbing fluid, ordinary commer- 

 cial nitric acid is saturated with potassic bichromate ; 

 this should be done in a warm room, as it takes up 

 much more when warm than when cold. The solu- 

 tion thus prepared is mixed with one-third of its 

 volume of sulphuric acid, and enough water added 

 to redissolve the chromic acid precipitated. 



T\vo objects are gained by adding the sulphuric 

 acid. The mixture is less expensive than if pure 

 nitric acid is used, and the internal resistance is de- 

 creased. If the internal and external cells are prop- 

 erly proportioned, this battery will run until the ex- 

 citing fluid is exhausted, without giving off any 

 fumes of nitrous acid. 



The Hooper Core and Wheatstone Apparatus. 

 In a contribution to Nature, on " Deep Sea 

 Baths," Mr. N. J. Holmes gives the preference 

 to what is called the Hooper core over the 

 gutta-percha core. Mr. Hooper's core is made 

 as follows : The copper conductor, after being 

 tinned, is coated with an insulation of pure In- 

 dia-rubber applied in the shape of a ribbon, 

 lapped spirally round it. Next, two strips 

 (one laid above and the other below) of India- 

 rubber, chemically prepared to resist the ac- 

 tion of sulphur, and called the " separator," 

 are applied so as completely to surround the 

 first rubber covering, as it were, with a tube ; 

 a pair of grooved die- wheels giving the con- 

 tour, and at the same time regulating accu- 

 rately the gauge of the core. Exterior strips 

 are then similarly applied of a compound of 

 rubber and a small percentage of sulphur. The 

 whole is then lapped round with water-proof 

 felt tape, and exposed for some hours in an 

 oven to a heat of about 383 F. By this pro- 

 cess the three successive coatings are welded 

 'Into one solid, dense, homogeneous mass, hav- 

 iug its distinctive features preserved as re- 

 gards the individual character of the several 



layers. Thus the heat, in driving off the sul- 

 phur from the outside coating, has converted 

 that envelope into an indestructible vulcanized 

 rubber jacket. The second layer, or " separa- 

 tor," has intercepted the passing of the sul- 

 phur by reason of its chemical properties, 

 while at the same time it has allowed an in- 

 finitesimal trace of the sulphur to combine 

 with the internal coating of pure rubber round 

 the conducting wire, sufficient to change its 

 character into an indestructible and non-lique- 

 fying material, without its becoming in any 

 way vulcanized. It is by this beautiful chemi- 

 cal affinity between the several layers, each 

 performing its special part toward the produc- 

 tion of one individual whole, that the " Hoop- 

 er insulation " has succeeded in establishing the 

 durability of the preparation. The advantage 

 of the Hooper core over the other is estimated 

 by the author in the proportion of 130 to 100 ; 

 that is, in a given time the former will trans- 

 mit 30 per cent, more words than the latter. 

 As regards apparatus for transmitting currents 

 through submarine conductors, Mr. Holmes 

 considers the Wheatstone automatic reading 

 system the most successful. He says : " By 

 this apparatus an average speed of over thirty 

 words a minute is regularly maintained upon 

 the Danish-English cable, a distance of 363 

 nautical miles, exclusive of a further land cir- 

 cuit of over 140 miles, making a total distance 

 of about 500 miles. This speed must be com- 

 pared with that of seventeen words per min- 

 ute, the highest result recorded over the same 

 circuit by the most improved Morse system. 

 From the results of the 'Wheatstone' appa- 

 ratus working over this circuit since Septem- 

 ber, 1868, it appears that, to obtain maximum 

 speed, the currents through a submarine cable 

 require to be transmitted of equal duration, at 

 equal intervals, in alternate directions, and 

 the line discharged to earth between each suc- 

 cessive reversal or current to neutralize the 

 charge, all cf which conditions are fulfilled in 

 the ' Wheatstone ' Automatic Jacquard ar- 

 rangement, which can only be compared to a 

 loom weaving the currents into the line, the 

 sequence of the currents representing the pat- 

 tern on the cloth. This apparatus is now 

 organized as the transmitting and recording 

 register upon the vast system of submarine 

 circuits belonging to the Great Northern 

 Telegraph Company, and the extensions from 

 Possiette Bay (Russian-Chinese frontier) to 

 Nagasaki, Shanghai, and Hong-Kong." 



Electric Novelties. Messrs. Bailey & Co., 

 of the Albion Works, Salford, England^ have 

 invented an ingenious contrivance for signal- 

 ling tbe state of high or low water at reser- 

 voirs, to any distant point. The two places 

 must be connected by telegraphic wires. A 

 float is then placed on the water, and as this 

 rises or falls it raises or depresses a lever, 

 which brings a finger-point into contact with 

 a platinized plate representing the line wire. 

 The battery is always fixed at an intermediate 



