326 Scientific Intelligence. 



Working between 63° and 130°, and 1900 atm., and upon 

 naphthalene, I found that the specific volume of the liquid on the 

 verge of solidification decreases as temperature increases, whereas 

 the specific volume of the solid on the verge of fusion increases 

 as temperature increases, the former variation being clearly much 

 more marked than the latter. Hence if temperature continually 

 increases, these loci tend to coalesce reproducing the essential 

 feature of Andrews's classical diagram, and pointing out the 

 occurrence of a lower or solid-liquid critical temperature in the 

 positive region of several thousand atmospheres and several hun- 

 dred degrees Centigrade. At this point liquid will pass to solid 

 and solid to liquid without change of specific volume and obvi- 

 ously without volume lag. In my data the initial or stable con- 

 tours of James Thomson's isothermals are also shown. 



Again I found the volume lag to be pronounced in its static 

 character. Hence the relations of solidifying point and pressure 

 and of melting point and pressure are not identical. If a march 

 be made in the direction of decreasing temperature, the prolonged 

 loci tend to intersect in a region of negative external pressure. 

 Beyond this therefore fusion takes place at a greater pressure 

 than solidification. This I interpret as follows: the normal type 

 of fusion changes into the ice type of fusion, through a transi 

 tional type characterized by the zero of volume lag. So far as I 

 can now discern, the position of the transitional type for naph- 

 thalene is below 50° C, and at about —3 000 atm. It is note- 

 worthy that the normal type is reached from the ice type, in a 

 direction of increasing temperature. 



7. Photoelectricity. — Prof. G. M. Minchin, at a meeting of the 

 Physical Society, Jan. 16, read a paper on the electromotive force 

 developed by light falling on sensitive plates which were immersed 

 in suitable liquids. The blue end of the spectrum was found to 

 be the most effective. Currents have a photographic effect on 

 the plates, and this action is strictly confined to the parts through 

 which the current has passed. Comparatively strong currents 

 were obtained from plates coated with eosine and gelatine. A 

 Hertz oscillator restored the sensitive state in a cell placed at a 

 distance of 81 feet. An arrangement of 50 cells in series with 

 an electrometer was exhibited, by means of which light falling on 

 the cells could generate sufficient e. m. f. to ring a bell or light 

 an electric lamp. — Nature, Feb. 5, 1891, p. 334. j. t. 



8. Photography of Colors. — According to M. G. Lippmann, the 

 essential conditions for photography in colors by his method are 

 (1) a sensitive film showing no grain ; (2) a reflecting surface at 

 the back of this film. Albumin, collodion, and gelatin films 

 sensitized with iodide or bromide of silver, and devoid of grain 

 when microscopically examined, have been employed. Films so 

 prepared have been placed in a hollow dark slide containing 

 mercury. The mercury thus forms a reflecting layer in contact 

 with the sensitive film. The exposure, development, and fixing of 

 the film is done in the ordinary manner, but when the operations 



