March ist, 1887.] 



SCIENTIFIC NEWS. 



17 



what way can the sensitiveness of the photographic plate 

 to the various rays be altered and controlled ? 



To a certain extent, a practical answer has been given 

 by the improved effect shown in Fig. 2, and this result has 

 been attained as follows : — A plale has been used in which 

 erythrosine has been introduced in the preparation, and 

 by means of this the blue, or chemical rays, have been 

 checked, whilst the other raj's have been made relatively 

 stronger. Further than this, a faint yellow screen is placed 

 between the object and the plate, to intercept a portion of the 

 chemical rays in the manner already referred to. 



Unfortunately, there is a great drawback to this process. 

 It is that no means have yet been devised for making the 

 visual and heat rays more chemically active. It is chiefly 

 by intercepting the powerful chemical rays, reflected by 

 the object, that the result is obtained ; but a prolongation 

 of the exposure must, of necessity, be resorted to. For 

 portraiture, this would be very objectionable, as it would 

 make pleasing expressions almost impossible ; and having 

 to be photographed would be voted more of a nuisance than 

 ever. Happily, in many other branches of photographic 

 work, a slightly prolonged exposure is in many cases of 

 no importance, and for copying pictures especially, the 

 orthochromatic plates can alone give an adequate represen- 

 tation of the painter's work. For " still-life," also, these 

 plates can be used with great advantage, and for certain 

 landscapes a decidedly more truthful representation and 

 more pleasing effects would be obtained. The subject 

 is, however, still far from being mastered, but the signs of 

 interest shown in this particular branch of photography bid 

 fair to be productive of very important results. 



Electrical Resistance of Metals at very Low Tem- 

 peratures. — The term " permanent gases " has ceased to 

 occur in the newer editions of our text-books of science. 

 Carbonic acid was condensed years ago. Hydrogen was 

 liquefied in 1879 by Pictet, and at the same time by Cail- 

 letet ; and one after the other of the so-called permanentgases, 

 and even our air, had to yield. The artificial cold produced 

 by the rapid evaporation of one of these gases has been made 

 use of to obtain the condensation of another gas. M. Wro- 

 blewski, who has distinguished himself in connection with 

 these experiments, has now tested the electrical resistance 

 of copper when exposed to the greatest cold he could obtain 

 — 201'^ Centigrade (330° Fahrenheit below zero). Spirals 

 of copper wire, covered with silk, were plunged directly 

 into the refrigerating liquids, and it was found that the elec- 

 trical resistance decreased more rapidly than the tempera- 

 ture. At the temperature mentioned, the electrical resist- 

 ance was only one-tenth of the resistance of the copper wire 

 at freezing point. MM. Cailletet and Bouty, experimenting 

 with the more moderate cold of 122° Centigrade, fully con- 

 firmed this decrease of resistance with decrease of tempera- 

 ture for silver, aluminium, tin, iron, copper, and other 

 metals ; also for mercury, which, when solid, has only one- 

 fourth of its resistance when liquid. It is noteworthy that 

 the formerly so-called permanent gases, hydrogen, nitrogen, 

 oxygen, etc., are electrically insulators \vhen in the liquid 

 state. 



Milk Infection. — The official report has now been published 

 of Mr. W. H. Power, Medical Inspector of the Local Government 

 Board, on the disease of cows which occurred in November and 

 December, 1S85, at a farm at Hendon, in Middlesex. The case 

 attracted much attention, as it was supposed that the cows 

 originated an infection which produced scarlet fever in those who 

 drank their milk. From the evidence given in this report it 

 seems to be conclusively established that the cow-disease did 

 actually cause scarlet fever in human beings. 



A Steam-propelled Torpedo. — Mr. Edward C. Peck, who 

 has charge of the draughting department at Yarrow and Co.'s 

 Torpedo Boat Works, has designed a fish torpedo to be propelled 

 by steam. It is of the usual Admiralty pattern outside, being 

 14ft. long by I4in. diameter, and it will carry loolb. of gun-cotton. 

 At about the centre is a hot-water reservoir, 4ft.. long and llMn. 

 internal diameter. This reservoir will be surrounded by a coat- 

 ing of non-conducting material Jin. thick, and between the out- 

 side and this and the skin of the torpedo will be a space of gin. 

 The reservoir is to be charged with about i6olb. of hot water 

 taken from the main boiler of the torpedo boat. The water will 

 be transferred very rapidly at a pressure of about 40Qlb. per 

 square inch, and there will be means for raising the temperature 

 of the water, if necessary, during its transfer from the boiler of 

 the boat to the reservoir of the torpedo. It is calculated that the 

 torpedo will keep steam for at least an hour after it has been 

 charged. The quantity of water carried will possess sufficient 

 sensible heat to supply the propelling engines with steam of a 

 slowly decreasing pressure during the run of the torpedo. The 

 space between the reservoir and the skin of the torpedo, as also 

 a portion of the space in the body of the torpedo not otherwise 

 occupied, is utilized as a surface condenser. By this means the 

 weight of the torpedo will be precisely the same at the close as 

 at the commencement of the run. The torpedo will be fitted 

 with engines of 6o-horse power indicated, and capable of pro- 

 pelling it through the water at a speed of 32 knots an hour. It 

 will be fitted with the usual fins, rudders, and regulating appara- 

 tus to insure its travelling at any required depth and in any 

 desired direction. The advantages of a steam-driven torpedo 

 are said to be very considerable. In the first place weight 

 is saved in the torpedo itself, and the pressure being only about 

 one-fourth of that in the Whitehead torpedo using compressed 

 air, there will be no difficulty in keeping all the joints and connec- 

 tions tight. It is also claimed that whereas compressed air will 

 only give a three-quarter minute run, steam will give a run of a 

 minute and three-ciuarters. The speed with compressed air is 

 24 knots, and the average range 600 yards, while with steam 

 Mr. Peck reckons on a speed of 32 knots and a range of 1,800 

 yards. 



Wire Nail Machine. — The manufacture of wire nails ex- 

 tends back about thirty years, and these nails, having originally 

 been made most extensively in France, are perhaps best known 

 as French nails. During the past ten or fifteen years the manu- 

 facture has been taken up by Germany, Belgium, and England. 

 The high cost of labour in England, however, as compared with 

 that on the Continent, has kept down the manufacture here. 

 The machines used in making these nails are practically the 

 same in all countries, only one nail being made at a time, and 

 the output being from 75 to 250 per minute, according to the size 

 of the nail being produced. The head of the nail is formed by 

 a blow, so that the machine is often laid up for repairs. A wire 

 nail-making machine on a new principle has recently been intro- 

 duced in this country. It is the invention of Mr. Clinton Lovell, 

 an American mechanic. This machine produces four nails at 

 once, the output being at the rate of from 400 to 1,200 per 

 minute, according to size, with a great saving of labour, power, 

 and space occupied. The machine is said to be positive in 

 its working and automatic in its action, drawing in the wire 

 from the reels, straightening it, feeding it into the machine, 

 cutting off the blanks, and carrying the blanks to the dies, where 

 they are pointed and headed, and thrown out completed. The 

 wire is never released from the first grip to the time the finished 

 nail is ejected. The whole of the operations in the machine are 

 performed by the simple pressure of the various parts, so that 

 jarring blows are avoided. After the ends of the coils of wire 

 arc inserted, the machine is automatic in its working. 



The Nordenfelt Submarine Boat was again tried last 

 month in the Bosphorus. She made a run completely sub- 

 merged, the only indication of her movements being a slight 

 disturbance of the surface from the ensign staff, purposely placed 

 so as to enable the committee to watch her course. The boat 

 carried, in addition to the engineers, several Turks. During the 

 trial she remained hermetically closed, the only steam power 

 used being drawn from the reservoir. 



Military Balloons. — It has been officially stated, in the 

 House of Commons, that a sum of two thousand pounds is to 

 be included in the Army Estimates, to be devoted to the de- 

 velopment of military ballooning. 



