156 REPORT — 1875. 



close of the year the Secretary visited M. Stas in Brussels, aud received 

 from hina details of the experiments which he liad made in testing the metal, 

 tlie results proving that the plate contained 999'95 parts of pure gold in 

 1000. The minute trace of foreign matter which is admixed with the gold 

 was probably derived from the clay crucible in which the finely divided metal 

 was melted. Mr. J. Norman Lockyer, F.E.S., has photographed the violet 

 and ultra-violet parts of the spectrum produced by the electric arc when 

 pieces of this gold are employed as terminals, side by side with the solar 

 spectrum ; and the result proves that neither silver, copper, nor iron, the 

 metals which might have jjeen expected to be present, exists in sufficient 

 quantity to be detected by the spectroscope. 



With the completion of this standard plate an important step has been 

 made in that a common ::tandard for reference has been secured. With 

 regard to the discrepancies between the results of different assayers, the 

 Committee propose to collect evidence in the hope of being able to ascertain 

 whether the causes of difference are introduced at the second or foi;rth 

 stages of the operation, or, in other words, in the furnace or while parting 

 with acid. 



Eifjhth Report of the Committee, consisting o/Prof. Everett, Sir W. 

 Thomson, F.R.S., Prof. J. Clerk Maxwell, F.R.S., G. J. Symons, 

 F.M.S., Prof. Ramsay, F.R.S., Prof. A. Geikie, F.R.S., James 

 (ilaisher, F.R.S., Rev. Dr. Graham, George Maw, F.G.S., W. 

 Pengelly, FR.S., S. J. Mackie, FG.S., Prof. Hull, FR.S., 

 Prof. Ansted, F.R.S., Prof. Prestwich, F.R.S., and C. Le Neae 

 Foster, appointed for the pmrpose of investigating the Rate of 

 Increase of Undeground Temperature doivmoards in various Locali- 

 ties of Dry Land and under Water. Draivn up by Prof. Everett, 

 Secretary. 



The supposed difficulties in the way of obtaining observations of temperature 

 in the St.-Gothard tunnel have vanished of themselves. On a recent visit to 

 the tunnel, your Secretary had the pleasure of meeting Dr. Stapff, who lias 

 for two years filled the post of official geologist to the " Direction "' of tlio 

 Gothard Eailway, and has in that capacity made the temperature of the tunnel 

 a special object of investigation. Dr. Stapff's observations are contained in 

 successive numbers of the Monthly and Quarterly Eeports of the Chief 

 Engineer to the " Direction," and of the Swiss Government Engineer to the 

 subventing States, on the progress of the Gothard Eailway. A^paper on the 

 subject was read by Dr. Stapff at a recent meeting of the Swiss Society of 

 Naturalists held at Andermatt in the immediate neighbourhood of the tunnel; 

 and an abstract of it has been kindly communicated by him to the Secretary, 

 accompanied with tables and diagrams. 



Dr. Stapff s observations were of three kinds : — ■ 



I. Observations of rock-temperature, made with very long thermometers, 

 inserted in horizontal bore-holes, of depth not exceeding one metre, in the sides 

 of the tunnel. The air was excluded by a firm plugging of taUow aU along 

 the stem, which was of such length that the scale projected into the air and 

 could be read without disturbing the instrument. They were graduated to 



