554 REPORT — 1894. 



masses of magnetite ever permanently magnetised ? Are large areas of surface 

 masses, saj' a few hundred square yards in extent, ever permanently and approxi- 

 mately uniformly magnetised in the same sense ? Is there any relation between 

 the geological age and the direction of the permanent magnetism of magnetic 

 rocks ? 



Inquiries such as these can only be taken up by individual workers, but I ven- 

 ture to think that the comparison of the observatory instruments and the fluctua- 

 tions of secular change outside the observatories could best be investigated under 

 the auspices of a great scientific society. The co-operation of the authorities of 

 the observatories will no doubt be secured, but it is most important that the 

 comparisons should in all cases be made with one set of instruments, and by the 

 same methods. Whether the British Association, which for so long managed a 

 magnetic observatory, maj' think that it could usefully inaugurate the work, it 

 would be improper for me in a presidential address to forecast. Who does it is 

 of less importance than that it should be done, and I cannot but hope that the 

 arguments and instances which I have to-day adduced may help to bring about 

 not only the doing of the work, but the doing of it quickly. 



The following Papers and Eeports were read : — 



1. Preliminary Experiments to find if Subtraction of Water from Air 

 Electrifies it. By Lord Kelvin, P.R.S., Magnus Maclean, M.A., 

 F.RS.E., and Alexander Galt, B.Sc, F.R.S.E. 



Experiments with this object were commenced by one of us in December 1868, 

 but before any decisive result had been obtained, circumstances rendered a post- 

 ponement of the investigation necessary. 



A glass u-tube with vertical branches, each 18 in. long and about 1 in. bore, 

 with the upper eight inches of one of the branches carefully coated outside and 

 inside with clean shellac varnish, was held fixed by an uninsulated support at- 

 tached to the upper end of this branch. The other branch was filled with little 

 fragments of pumice soaked in strong pure sulphuric acid or in pure water ; and a 

 fine platinum wire, with one end touching the pumice, connected it to the insu- 

 lated electrode of a quadrant electrometer. A metal cylinder, large enough to 

 surround both brandies of the (j-tube without touching either, was placed so as 

 to guard the tube from electric influences of surrounding bodies (of which the 

 most disturbing is liable to be the woollen cloth sleeves of the experimenters or 

 observers moving in the neighbourhood). This metal tube was kept in metallic 

 connection with the outside metal case of the quadrant electrometer. The length 

 of the exposed platinum wire between the u-tube and the electrometer was so 

 short that it did not need a metal screen to guard it against irregular influences. 

 An india-rubber tube (metal, metallically connected with the guard cylinder, 

 ■would have been better) from an ordinary blowpipe bellows was connected to 

 the uninsulated end of the y-tube. Air was blown through it steadily for nearly 

 an hour. With the sulphuric pumice in the other branch the electrometer rose in 

 the course of three-quarters of an hour to about nine volts positive. When the 

 pumice was moistened with water, instead of sulphuric acid, no such effect was 

 observed. The result of the first experiment proves decisively that the passage of 

 the air through the jj-tube gave positive electricity to the sulphuric acid, and there- 

 fore sent away the dried air with negative electricity. A corresponding experiment 

 with fragments of chloride of calcium instead of sulphuric pumice gave a similar 

 result. In repetition of the experiments, however, it has been noticed that the 

 strong positive electrification of the (j-tube seemed to commence somewhat sud- 

 denly when a gurgling sound, due to the bubbling of air through free liquid, 

 whether sulphuric acid or chloride of calcium solution, in the bend of the u-tube, 

 began to be heard. We intend to repeat the experiments with arrangements to 

 prevent any bubbling of the air through liquid. 



We have repeated our original experiment with pumice moietened with water 



