420 



Anniversary Meeting. 



[Dec. 1, 



attained, and those in whicli the stratified discharge is displayed. Of the 

 delicacy and beauty of the experiments it is not necessary here to speak, 

 for they have been already exhibited here, as well as to more than one 

 audience on a large scale. Through this advance on his part, a help- 

 ing hand will doubtless be held out to those who are occupied with 

 the subject of stratification ■ for in this matter, the two advancing 

 powers desire neither a "neutral zone" nor a "scientific frontier" 

 to separate their field of action. 



Another communication, full of promise as well of performance, 

 should also not pass unnoticed. I allude to Professor Hughes' paper 

 on his Induction Currents Balance, the application of which has already 

 branched out and borne fruit in more than one direction. The ex- 

 treme simplicity of the instruments, and their marvellous adaptation 

 to the purposes for which they were intended, reflect the highest 

 credit on their inventor. 



Not unconnected with Mr. Crookes' researches, so far as they are 

 directed towards the ultimate constitution of gases, are those of Pro- 

 fessor Osborne Reynolds. In his remarkable paper, "On Certain 

 Dimensional Properties of Matter in a Gaseous State," Professor 

 Osborne Reynolds has established the fact of what he calls Thermal 

 Transpiration, namely, that when two portions of the same gas are 

 separated by a porous plug, the two surfaces of which are of different 

 temperatures, the condition of equilibrium is no longer that the pres- 

 sures of the gas on the two sides of the plug should be equal, but that 

 the pressure on the hotter side should exceed that on the colder side 

 by a certain quantity ; and that if this is not the case, the gas will 

 transpire through the plug until this condition is satisfied. Professor 

 Reynolds connects this principle with Mr. Crookes' Radiometer 

 experiments ; and the various considerations which he brings to bear 

 on the subject appear to have this idea throughout, that the dynamical 

 similarity of two gaseous systems, bounded by solid surfaces, geome- 

 trically similar, depends on the ratio of the homologous lines of the 

 system ^to a certain quantity, having the dimensions of a line, and 

 which varies inversely as the density of the gas. Although dimen- 

 sional considerations have been shown by previous writers to have an 

 important bearing on the Theory of Gases, still his experimental re- 

 sults form an important contribution to our knowledge of the subject ; 

 and in his theoretical investigation he has attacked, with vigour, and 

 not without success, some elements of the problem avoided by his pre- 

 decessors in this field of research. 



Photography has of late years become so completely the handmaid 

 of Physical Science, and has so constantly responded to the calls of its 

 master, that its progress, however rapid and however effective, has come 

 to be taken almost sk a matter of course. But the step which Captain 

 Abney appears now to have taken lies entirely out of the ordinary line 



