20 REroRT— 1898. 



and aspirations. Tlie low temperature researches whicli bring such 

 renown to Professor Dewar and to his hiboratory in the Royal Institution 

 have been crowned during the present year by the conquest of one of 

 Nature's most defiant strongholds. On the 10th of last INlay Professor 

 Dewar wrote to me these simple but victorious words : ' This evening I have 

 succeeded in liquefying both hydrogen and helium. The second stage of 

 low temperature work has begun.' Static hydrogen boils at a temperature 

 of 238° C. at ordinary pressure, and at S-jO' C. in a vacuum, thus enabling 

 us to get within 23'' C. of absolute zero. The density of liquid hydrogen 

 is only one-fourteenth that of water, yet in spite of such a low density it 

 collects well, drops easily, and has a well-defined meniscus. With proper 

 isolation it will be as easy to manipulate liquid hydrogen as liquid air. 



The investigation of the properties of Ijodies brought near the absolute 

 zero of temperature is certain to give results of extraordinary importance. 

 Already platinum resistance thei-mometers are becoming useless, as the 

 temperature of boiling hydrogen is but a few degrees from the point 

 where the resistance of platinum would l)e practically nothing, or the 

 conductivity infinite. 



Several years ago I pondered on the constitution of matter in what I 

 ventured to call the fourth state. I endeavoured to probe the tormenting 

 mystery of the atom. What is the atom ? Is a single atom in space 

 solid, liquid, or gaseous. Each of these states involves ideas which can 

 only pertain to vast collections of atoms. AYhether, like Newton, we try 

 to visualise an atom as a hard, spherical body, or, with Boscovitch and 

 Faraday, to regard it as a centre of force, or accept the vortex atom theoiy 

 of Lord Kelvin, an isolated atom is an unknown entity diflicult to conceive. 

 The properties of matter — solid, liquid, gaseous — are due to molecules 

 in a state of motion. Therefore, matter as we know it involves essentially 

 a mode of motion ; and the atom itself — intangible, invisible, and incon- 

 ceivable — is its material basis, and may, indeed, be styled the only true 

 matter. The space involved in the motions of atoms has no more preten- 

 sion to be called matter than the sphere of influence of a body of riflemen 

 — the sphere filled Mith flying leaden missiles — has to be called lead. 

 Since what we call matter essentially involves a mode of mction, and 

 since at the temperatui-e of absolute zero all atomic motions would stop, 

 it follows that matter as we know it would at that paralysing temperature 

 probably entirely change its properties. Although a discussion of the 

 ultimate absolute properties of matter is purely speculative, it can hardly 

 be barren, considering that in our laboratories we are now within moderate 

 distance of the absolute zero of temperature. 



I have dwelt on the value and importance of nitrogen, but I must not 

 omit to bring to your notice those little known and curiously related 

 elements which during the past twelve months have been discovered and 

 partly described by Professor Ramsay and Dr. Travers. For many years 

 my own work has been among what I may call the waste heaps of the 



