I82 



NATURE 



[April 8, 1920 



the form of circular discs about 2 cm. thick and 

 25 cm. in diameter enclosed in a porcelain tube between 

 iron cylinders of the same diameter. In the upper iron 

 cylinder heat was generated by a measured electric 

 current. The fall of temperature through the disc 

 was determined by means of thermo-couples. For tin, 

 lead, zinc, and aluminium the heat conductivity de- 

 creases gradually up to the 'melting point. At the 

 melting point the conductivity decreases abruptly, but 

 in the liquid state its rate of decrease with increase of 

 temperature is slight. Bismuth increases in conduc- 

 tivity on melting, but change of temperature has little 

 effect on the conductivity in either the liquid or the 

 solid state. Antimony has its maximum conductivity 

 at the melting point. In all cases the electrical and 

 heat conductivities change in the same direction on 

 melting, but neither above nor below the melting 

 point does their quotient agree with electronic theories. 



The trouble of working- gelatine plates under tropi- 

 cal conditions seems at last to have been overcome. In 

 the Journal of the Royal Photographic Society for 

 March, Mr. A. P. Agnew, of Messrs. Ilford, Ltd., 

 describes the " Ilford tropical hardener " that is now 

 supplied by Messrs. Johnson and Sons. Mr. Agnew 

 found that a "quite weak solution of formalin" 

 became very effective when certain salts were dissolved 

 in the solution. Many sodium salts were found useful, 

 while potassium and magnesium salts are not so effec- 

 tive, and ammonium salts are unsuitable. Some salts 

 have no effect, while chlorides, bromides, and nitrates 

 in general have an opposite action— that is, they soften 

 the .gelatine. The exposed plate is put into the suit- 

 ably diluted hardening solution for three minutes, then 

 rinsed and developed, etc., as usual. Plates so treated 

 at temperatures varying from ioo° to more than 

 140° F., then fixed in a plain hypo solution at 40° F., 

 and finally washed for two hours at more than 100° F. 

 remained firm and did not even show signs of reticula- 

 tion. Such trying conditions as these would never 

 occur in practical work. 



A PHOTOGRAPHIC developing agent must be able to 

 reduce silver bromide that has been changed into the 

 developable condition, as by exposure to light, while 

 under the same conditions it is unable to reduce silver 

 bromide that has not been so changed. There are 

 many reducing agents that make no distinction 

 between these two states of silver bromide. Some 

 twenty years ago Messrs. A. and L. Lumi^re found 

 certain details of chemical constitution that appear to 

 confer developing power, and since then they and 

 others have extended the investigation. In the British 

 Journal of Photography for March 26 there appears 

 a translation of a paper by Dr. Seyewetz(of Lumi^re's) 

 in which the author summarises our present know- 

 ledge of this matter. Knowing the necessary con- 

 stitution, a very large number of developers have 

 been introduced and actually put upon the market, 

 but the greater number have commercially disappeared, 

 because in some way or other they were incon- 

 venient to use. Dr. Seyewetz says that it is improb- 

 able that new developers will displace those now in 

 common use. As in the case of dyes, it seems difficult 

 NO. 2632, VOL. 105] 



to make sensational discoveries, and there is so far 

 no indication of the direction in which to seek for 

 new developers that would prove acceptable, as, for 

 example, by permitting a reduction in the period 

 of exposure. 



Besides the paper on H.M.S. Hood, read at the 

 recent meeting of the Institution of Naval Architects 

 by Sir Eustace d'Eyncourt, there are important articles 

 in the Engineer and Engineering for March 26 dealing 

 with this ship. The building was commenced in 

 April, 19 16, at the Clydebank yard of Messrs. John 

 Brown and Co., Ltd., the first of the main belt 

 armour-plates (32 tons each) reached the yard in June, 

 1918, the ship was launched on August 22, 1918, 

 and the fitting out was completed in January of this 

 year, when the huge ship passed down the Clyde to 

 the open sea. On the trial trips the turbines developed 

 157,000 shaft-horse-power, the speed attained being 

 32 knots. The overall length is 860 ft., the extreme 

 breadth 104 ft., the mean load draught 28-5 ft., 

 and the displacement at load draught 41,200 tons. 

 The hull is fitted with a bulge or blister for securing 

 the ship against effective attack by torpedo. The 

 armour ranges from 12 in. thick amidships to 5 in. aft. 

 The deck over the magazines is 3 in. thick. There 

 are eight is-in. guns, all on the middle line, each 

 pair being mounted in an armoured barbette. The 

 secondary armament consists of twelve 5-5-in. guns, 

 and there are four 4-in. anti-aircraft guns mounted 

 on the superstructure. The ship is fitted with six 

 torpedo tubes for 21-in. torpedoes. There are eight 

 electric generators, four of which are driven by re- 

 ciprocating engines, two by geared high-speed impulse 

 turbines, and two by eight-cylinder Diesel oil engines. 

 About 360 electromotors are installed, ranging from 

 i' to 140 brake-horse-power. 



Sir Alfred Ewing is bringing out almost imme- 

 diately, through the Cambridge University Press, a 

 treatise on "Thermodynamics for Engineers," in which 

 the author aims at making readers familiar with the 

 physical bearing of the fundamental ideas of the subject 

 by means of an elementary introduction and by dealing 

 with practical problems in the theory of heat-engines 

 and of refrigeration. A more mathematical treatment 

 of general thermodynamic relations follows. There 

 will also be an appendix sketching in outline the 

 molecular theory of gases, with special reference to 

 internal energy and specific heat. Another book on 

 the list of the Cambridge University Press is by Prof. 

 A. S. Eddington, entitled " Space, Time, and Gravita- 

 tion." It is promised for the coming summer. 



A FORTHCOMING addition to Sir Edward Thorpe's 

 series of Monographs on Industrial Chemistry is of 

 current interest, seeing that it will treat of "The 

 Manufacture of Sugar from the Cane and Beet." It 

 will be by T. H. P. Heriot, of the Royal Technical 

 College, Glasgow, and give special attention to the 

 principles underlying factory operations. 



Erratum.— On p. 138 of Nature of April i, col. i, 

 line 15 from the bottom of the page, bx should be 

 dx-2 in the equation y=^axi + bxl The fractional index 

 was broken during paging of the issue. 



