606 SCIENTIFIC RECORD FOR 1885. 



The emissive power of a surface increases markedly when it is depol- 

 ished. This fact Christiansen accounted for on the theory that such a 

 surface sent out not only the heat emitted directly but also the heat 

 emitted and then reflected. To test this theory he constructed a cube 

 one face of which was plane, another corrugated, the corrugations hav- 

 ing sharp angles and the sides inclined 90° to each other, a third sim- 

 ilarly corrugated but with the inclination 45°, and a fourth containing a 

 large number of conical cavities. All these surfaces were equally pol- 

 ished and their emissive powers normal to the faces of the cube were 

 1, 2*05, 2'66, and 8-7, respectively. The apparent emissive power of the 

 conical cavities is approximately the same as that of a surface equal to 

 the sum of their bases covered with lampblack. ( Wied. Ann., xxi, 364 ; 

 J. Phys., November, 1885, II, iv, 528.) 



Kontgen appears to have settled the disputed question of the absorp- 

 tion of heat by the vapor of water by the following neat experiment : 

 A thick tube of brass, gilded, is closed at one end by a plate of rock 

 salt. If now it be exposed to a source of heat, the heating will depend 

 (1) upon the heat transmitted by the walls of the tube and (2) upon the 

 heat absorbed by the gas. Place the interior of the tube in commu- 

 nication with a Marey's manometric capsule, the style of which rests on 

 the surface of a recording cylinder. Under the above circumstances it 

 will record an increase of pressure which will be permanent if the heat- 

 ing is due to the first cause and transient if due to the second. The 

 secoud effect is observed when the tube contains air saturated at zero 

 and then heated to 26°, the increase of pressure due to the heating of 

 the gas being 2-18'"™. A much less increase was observed with air con- 

 taining carbon dioxide in the normal proportion of the atmosphere. 

 The source of heat in these cases was a Bunsen burner. ( Wied. Ann., 

 XXIII, 1, 259 ; J. Phys., April, 1885, II, iv, 181, 529.J 



Clark has devised a radiant energy recorder dej^ending on the evap- 

 oration of water in vacuo. The instrument is essentially a Wollaston 

 cryophorus in which the vertical tube and lower bulb are replaced by a 

 simple glass tube graduated in cubic centimeters. The bulb containing 

 the water to be evaporated is blackened by holding it in the smoke of 

 burning camphor and is then exposed to the sun, the rest of the appa- 

 ratus being silvered or properly protected by sheets of bright tin. At 

 sunset the water which has distilled over can be read off on the graduated 

 tube and expressed in heat units. {Nature, July, 1885, xxxii, 233.) 



According to Lommel's theory of fluorescence there should be an ab- 

 sorption band in the spectrum of esculin in 'the vicinity of the line A. 

 Wesendonck has examined this part of the spectrum by means of phos- 

 phorographs and has been unable to recognize any such band in that 

 region. ( Wied. Ann., xxiii, 548 ; J. Phys., November, 1885, II, iv, 533.) 



Velten has measured the specific heat of water at ordinary tempera- 

 tures, using (1) the method of mixtures and (2) an ice calorimeter. 

 The results are quite complex but the formula which appears to the 



