KINKTIC OR MECHANICAL VIEW OF XATUKE. 55 



found in Lord Kelvin's celebrated lialtinuiie l>.'eture8 ^ 

 where with unhinittMl resourcefulness the methods of ' 

 analogy, analysis, and experiment are employed to solve 

 or to define the intricate problems of pliysical optics. 

 Nor is it a merely fortuitous coincidence for the history 

 of thought that, whilst his mind must have been filled 

 with the many illustrations and mechanical devices, and 

 all the wealth of suggestions contained in the Baltimore 

 Lectures, Lord Kelvin should have delivered the opening 

 address to the mathematical section of the Ihitish Asso- 

 ciation, entitled, " Steps towards a Kinetic Theory of 

 ]\Iatter." Following — as did also Clerk Maxwell — on 

 the lines indicated by Stokes's earlier papers, he has done 

 much to change our fundamental conceptions as to the 

 properties of matter, and this in two distinct ways. 

 The first consisted in breaking down the rigid barriei-s 

 which popular definitions had set up between the dif- 

 ferent forms of aggregation — the solid, liquid, and gaseous 

 states of matter ; whilst the second tended to show how 



^ The Baltimore Lectures were 

 delivered by Lord Kelvin (then Sir 

 \V. Thomson) after the meeting of 

 the British A.ssociation at Montreal 

 in the month of October 1884, at 

 the Johns Hopkins University, be- 

 fore a company of physicists. The 

 final edition of these important and 

 highly suggestive conferences is in 

 the press as the fourtli volume of 

 the collected mathematical and 

 physical pajiers. The comjjletion 

 of this publication is eagerly ex- 

 pected, as containing the most 

 mature exposition of the elastic- 

 solid tlieory of light, towards which 

 the author has in the course of the 

 last fifteen years made various valu- 

 able additions. Notably in a paper 



dated 1888, published in the ' I'liil- 

 osophical Magazine,' he has, as it 

 has been said, " extricated the 

 elastic theory from the position of 

 deadlock, according to which the 

 ether must be botii compressible 

 and incompressiljle," by showing 

 that the difficulty can be met, " pro- 

 vided we either sujjpose the medium 

 to extend all through boundless 

 space, or give it a fixed containing 

 vessel as its boundary." I'mf. 

 Glazebrook has further worked out 

 the consequences of this suggestion. 

 See vols. 26 and 27 of the .'ith series 

 of the ' Phil. Mag.,' also ^ Nature.' 

 vol. 40, 1889, i>. 32, and Fletcher, 

 the ' Optical Indicutrix,' p. (J, ic. 



