ON UNDERGROUND TEMPERATURE. 23 



perature at this depth from his own observations, and the temperatures at 

 77, 119, and 382 feet from the subsequent observations of the merchant to 

 whom the well belonged. His figures differ very materially from those given 

 above ; but it may fairly be presumed that General Helmersen's account is 

 the more accurate. 



Before the receipt of General Helmersen's letter, <;he following communi- 

 cation respecting the Moscow boring had been received by the Secretary from 

 Mons. N. Lubimoff, Professor of Natural Philosophy in the University of 

 Moscow. 



" December ^^, 1870. 



" Dear Sir, — I beg your pardon for not having replied sooner to your letter. 

 I am sorry to say that the information which I can now communicate is very 

 deficient. The great bore of Moscow is not yet terminated, and the experi- 

 ments on temperature which have been made hitherto are but of a preli- 

 minary kind. It was in the hope of renewing the measurements under more 

 satisfactory conditions that I delayed my answer ; but as certain circum- 

 stances did not permit me to resume the observations, which are therefore 

 deferred to the spring of 1871, 1 must restrict myself to describing the old ones. 



" These were made, on my commission, by M. Schiller, B.A., in April 1809. 

 The bore was then about 994 feet deep, and, from 56 feet to the bottom, 

 full of water. A mercury thermometer of a peculiar kind was constructed, 

 on an idea of my own. It consisted of a capillary tube of thick glass, ter- 

 minating below in a large reservoir ; at the upper end a funnel-like piece 

 was adjusted, into which the mercury flowed off as soon as the temperature 

 rose above a certain value [sketch annexed]. The whole was placed within 

 a closed case, which was plunged to a chosen depth into the bore, and re- 

 versed by means of a special arrangement. It was then brought again to the 

 right position and drawn up to the surface, a poftion of mercury having 

 flowed away. Here the thermometer was plunged into a water-bath, the 

 temperature of which was so regulated that the mercury attained the end of 

 the capillary tube ; this was then the temperature required. 



" The measurements were made at the depths of 175, 350, 525, 700, 875, 

 and 994 feet. From 350 feet to the bottom the temperature throughout the 

 bore was found to be nearly constant, namely 10°'l C, with deviations of 

 + 0°-l. The temperatures of the upper parts of the bore were not quite 

 precisely ascertained, the chief attention being given, in these first experi- 

 ments, to the deeper parts. The air-temperature at the surface for the time 



( 



11 April to ?^4^^ varied between -f-7°-5 and -l°-9 C. 

 29 ^ 5 May / 



" As soon as the boring is completed, and the present impediments removed 

 from the bore, the observations will be resumed, and perhaps some new 

 methods will be applied for the sake of verification, though the above de- 

 scribed apparatus, previously tried, seemed to give very exact results. 



" I shall be very glad to communicate to you, as soon as possible, the re- 

 sults of the new experiments. As to underground temperatures for Russia 

 in general, there is, so far as I know, no place where regular and trustworthy 

 observations have been made {^should be made in original] except the Central 

 Physical Observatory at St. Petersburg, the results of which are published by 

 Dr. Wild, Director of the establishment, in his printed Annual Reports." 



From the sketch annexed to the description in Professor Lubimoff's letter, 

 it appears that the enlargement at the open end of the capillary tube is quite 

 sudden, and not likely to retain any mercury when inverted. The idea of 

 error from this cause may therefore be dismissed ; but the instrument is en- 



