124 



NATURE 



[Dec. 14,1871 



attempt at equilibration they are more or less counteracted or as- 

 sisted by otlier natural forces. 



"As an illustration I would recognise every special issue of evo- 

 lution, as, for example, some well-marked variety of animal (say 

 pigeon) or plant (say rose) as the effect of the combination of the 

 usually so-called natural forces in conjunction with the evolutive, 

 as a temporary stable form, so long as environing conditions to 

 which it was subjected remain the same. Hence appears the 

 permanency of some species and races. Subject them, however, 

 to altered conditions, and thus bring an unaccustomed set offerees 

 to bear upon them, e.g., by domestication or cultivation; the 

 forrrs once so stable soon ' break,' the equilibrium is overthrown, 

 and variations once more ensue 



"After all, therefore, what I have here called evolutive forces in 

 the organic world may prove to be only particular phases of those 

 which conspire to constitute animal and vegetable life. And just 

 as in the vital force itself it is usual to recognise two such phases, 

 viz., the vegetative and reproductive, so the power of develop- 

 ment or continual advance or alteration from an assumed type 

 may ultimately appear as particular forms of life-force 

 it suing in those results which we are accustomed to look upon as 

 designed." George Hknslow 



ON DEEP-SEA THERMOMETERS* 



THE objects of this paper and of the experiments and 

 observations recorded therein, are : — 



1. The ascertainment of the effect of pressure on ther- 

 mometers used for deep- sea purposes. 



2. To obtain a scale whereby observations made by 

 the thermometers now in use could be corrected for 

 pressure. 



3. To obtain a scale whereby observations made pre- 

 viously by other thermometers can be utilised. 



In the early part of the year 1868 the attention of the 

 Hydrographer of the Navy was directed to the unsatis- 

 factory nature of the deep-sea Six's thennometers then 

 in use. 



The objections made to these thermometers were : — 



1. Their fragility, the slightest jar or blow often break- 

 ing them. 



2. The necessity of their being always kept in a vertical 

 position. 



3. The uncertainty of the register, the indices being 

 generally capable of being shaken down. 



4. Their large size, in connection with friction in passing 

 through the water. 



5. The substance they were mounted on, being generally 

 wood, became so swollen by pressure of the water as 

 often to render them incapable of being withdrawn from 

 the case. 



It was also considered that in all thermometric obser- 

 vations at great depths we had been " working in the 

 dark," in that we had no idea of the effect pressure had 

 on the instrument, and consequently on the recorded 

 results ; and it was reasonable to suppose that as the 

 action of a thermometer was affected in vacuo, an opposite 

 effect would be had by placing them under pressure, the 

 more especially as in the one case the pressure of only one 

 atmosphere, or 151b. to the square inch, was removed, 

 while in the other the atmospheres would have to be 

 reckoned by hundreds and the pressure by tons. On this 

 point we were not without actual observation ; for Mr. 

 Glaisher, during the year 1844, in some experiments made 

 on the temperature of the Thames near Greenwich with 

 delicately constructed instruments, found that the indica- 

 tions of temperature were affected by pressure on the bulb 

 of the thermometers, and that at a depth of only 25 feet, 

 or about three-fourths of an atmosphere, the readings were 

 increased by z' ; but no definite conclusion could be 

 arrived at from these observations in respect to our deep- 

 sea thermometers, beyond the fact that they were liable to 

 be so affected. 



* Abridged from a paper read before the Meteorological Society, April 

 19, 1871, by Capt. J. E. Davis, R.N. 



It was therefore suggested to the Hydrographer — 



1. That the author might be placed in personal com- 

 munication with different makers in respect to the best 

 construction for the purpose required ; and 



2. That a series of experiments should be made by 

 placing some thermometers in a hydraulic press in con- 

 junction with one in an hermetically sealed iron bottle (as 

 a standard) and subjecting them to pressure, that they 

 should be kept under pressure sufficient time to allow the 

 thermometer within the bottle to take up the temperature 

 without, and then the whole compared Avith the standard. 



The first suggestion was immediately acceded to ; and 

 those makers from whom the Meteorological Department 

 obtained instruments were applied to, and a list of deside- 

 rata submitted to each. Three makers responded, and six 

 instruments were ordered from each. 



These instruments were sent in (hereafter called the 

 Hydrographic Office pattern), and Mr. Balfour Stewart, of 

 the Observatory at Kew, was consulted as to the modus 

 operandi of testing by pressure, and he approved of that 

 already suggested. 



A difficulty arose in respect to a hydraulic press —the 

 use of some in London could not be obtained, and others 

 were not adapted to the purpose, so that the testing was 

 deferred, and some of the instruments were sent to 

 H.M.S. Gannct, then deep-sea sounding on the edge of the 

 Gulf-Stream, and afterwards some to H.M.S. Lightning 

 for her dredging cruise. 



On the return of these vessels the conflicting nature of 

 the temperatures obtained from those supposed to exist 

 (as derived from observations in other localities) rendered 

 the necessity of ascertaining the nature and amount of 

 error due to pressure the more imperative. 



At this juncture Mr. Casella undertook to have a testing 

 apparatus constructed at his own expense, capable of pro- 

 ducing a pressure of three tons to the square inch. 



At a meeting of the Committee of the Royal Society, 

 held in the Hydrographer's Room in April, i86g, and at 

 which the plan of operation for testing the thermometers 

 was discussed, that by means of an iron bottle approved. 

 The late Dr. Miller, V.P.R.S., proposed encasing the full 

 bulb in an outer covering of glass containing air, in order 

 to permit the lighter fluid (air) to be compressed without 

 affecting the bulb within, and one such was directed to be 

 made ; but instead of the outer casing being filled with 

 air it was nearly filled with alcohol, which being heated to 

 reduce the quantity of air, the bulb was then hermetically 

 sealed. Mr. Casella was also directed to make others 

 that would facilitate the observations. 



At the time these experiments were proposed, it was not 

 known that a thermometer had been constructed, at the 

 suggestion of Mr. Glaisher, by the late Admiral Fitzroy's 

 directions, with the view of removing the difficulty of 

 pressure ; this was done by encasing the long bulb at the 

 back of the instrument in glass, and nearly filling the 

 space between the case and the bulb with mercury;* and 

 one on this principle was then in the Instrument-room of 

 the Meteorological Office ; but although some had been 

 used for deep-sea purposes, the further issue of them had 

 been stopped on account of their fragility, and thus the 

 means for obtaining accurate observations were virtually 

 the same as before. 



It was decided to test them at pressures equal to the 

 following depths in the ocean, viz., 250, 500, 750, 1,000, 

 1,250, 1,500, 1,750, 2,000, 2,250, and 2,500 fathoms, the 

 rule to be applied being 33 feet = one atmosphere = 15 lb. 

 on the square inch. From this a table was constructed 

 for use. 



On the 4th of May the following thermometers were 

 taken to Hatton Garden, viz. : — • 



Nos. 56 and 57 Casella . Hydrographic Office pattern. 

 66 and 67 Elliott . . „ „ „ 



72 and 73 Pastorelli. „ „ „ 



* See Meteciological Papers, No. I., 1S63. 



