Chemistry and Physics. 393 



The greater part of these two E.M.F.'s are considered as due to 

 thermo-electric forces* and special experiments are noted which 

 support this view. — Proc. Hoy. Soc, No. 450, p. 512. 



13. Unsolved Problems in Low- Temperature Research. — An 

 essay by Miss Agnes M. Clerke, author of " A Popular His- 

 tory of Astronomy during the Nineteenth Century," upon Low- 

 Temperature Research at the Royal Institution of Great Britain, 

 1893-1900, has recently been issued. It gives an admirably 

 clear and complete summary of this most interesting subject, 

 and closes with the following chapter. 



"The development of low-temperature chemistry is one of the 

 most striking features of scientific history during the last decade 

 of the nineteenth century. Many questions of profound interest 

 have been answered through its means, and a partial insight has 

 been gained into some of the most recondite secrets of nature. 

 The unique condition attends it, that the ne plus ultra cannot 

 recede as it advances. The absolute zero forms an irremovable 

 landmark, a boundary line that may not be transgressed, an 

 asymptote, as it were, to the curve of future progress. And 

 every step nearer to it is harder to take than the previous one. 

 Among many causes of augmenting difficulty is the circumstance 

 that the molecular latent heats of vaporization diminish with the 

 absolute boiling point. Hence, a continually more lavish expendi- 

 ture of frigorific material is necessitated, and of material the 

 price of which, in money and labor, rises rapidly with its 

 frigorific efficacy. Still, although the bottom of the tempera- 

 ture-scale may never be actually reached, the intervening space 

 will surely be much abridged. But we c^all never, it is safe to 

 predict, assist at the ' death of matter/ At the stage arrived at, 

 there is no sign of its being moribund. Forces still act within 

 and upon it. Gravity and cohesion maintain their normal power. 

 It sensibly impedes the passage of electricity in the purest and 

 most highly conducting metals. Its minute particles can take up 

 and modify luminous vibrations. Only chemical affinity seems 

 to be extinct ; the various species of matter cease to react upon 

 each other. The next cryogenic achievement, it is true, may 

 alter the situation as we now see it. Our present standing- 

 ground maybe subverted, for the inquiry is just now in a critical 

 phase. The liquefaction of helium, for example, may prove 

 decisive of many things — it may set at rest some doubts, and 

 raise unlooked-for issues. 



The conditions for its accomplishment were clearly set forth 

 in the Bakerian Lecture. They may be realized by the use of 

 methods actually available. This last fortress of gaseity cannot 

 be regarded as impregnable, although its capture will be at a 

 high monetary cost. Gaseous helium, to begin with, is of the 

 utmost scarcity ; and what is scarce demands outlay to procure. 

 Its condensation can be effected only by subjecting it to the 

 same process that succeeds with hydrogen, substituting, how- 

 ever, liquid hydrogen under exhaustion for liquid air as the pri- 



