May 23, 1878] 



NATURE 



93 



second law of thermodynamics is not violated, as it would be if 

 the diaphragm effected only an unequal distribution of energy. 

 The great point, however, to notice is that the sifting power of 

 the diaphragm enables us to derive work from • the • gas at the 

 expense of its heat, or we obtain thereby a capacity for work 

 without the performance of work, which is the practical result 

 Ve require, and so long as we obtain this result, we may not 

 care so much about any inquiry whether a certain statement of a 

 law is thereby violated or not (at least this inquiry is of secondary 

 importance). The main point evidently is to realise how work 

 may be derived from normal temperature heat without a source 

 or refrigerator. Also it cannot surely be kept too much in view 

 that the "second law of thermodynamics " is not theoretically a 

 necessary truth, but its truth only depends (as Prof. Maxwell 

 showed) on our inability to -grasp or handle molecules. For if 

 molecules were of such a size that we could handle them sepa- 

 rately, then there is no doubt that we could transfer their motions 

 to masses (without the necessity for mixing the molecules of 

 different masses together). The attempts to prove the second 

 law of thermodynamics as an abstract truth independently of 

 considering the violecular state of matter, can therefore scarcely 

 be considered as .legitimate, as it is upon the molecular state of 

 matter that the impracticability of the effect expressed in the law 

 depends. Also it would be, perhaps, difficult to give a perfectly 

 satisfactory d. priori proof that no process can be discovered for 

 utilising normal temperature heat without permanently mixing or 

 altering the distribution of the matter concerned, more especially 

 when it is considered how much can be already done in the way 

 of manipulating molecules (or fifting their velocities) and 

 deriving their heat by means of porous diaphragms in the case of 

 diffusion. The practicability of the result would admittedly not 

 be contrar)' to the principle of the conservation of energy. 



6. One of the most important considerations, perhaps, connected 

 with diffusion, would appear to be that the tendency to the uniform 

 diffusion of matter, or rather of velocity [since chemically 

 different molecules of equal mass do not necessarily tend to 

 become uniformly diffused], can upset the tendency to the uniform 

 difiiision of energ)', i.e., energy could not be uniformly diffused 

 until matter (capable of diffusion) was also uniformly diffixsed, or 

 homogeneous. Another important consideration would appear 

 to be (and which, if noticed, would seem to be worthy of greater 

 attention) that the gases of the atmosphere from the fact of their 

 being of different molecular weights, tend forcibly to become 

 uniformly diffused, or the danger of unequal mixture is averted, 

 which would inevitably occur sometime or somewhere, if the 

 gases were of the savie molecular weights (or dynamically alike), 

 and so diffusion were left to the pure contingencies of chance. I 

 may return (by permission of the Editor) to this point at a future 

 opportunity. S. Tolver Preston 



''Underground Temperature" 



The Report of the British Association Committee on Under- 

 ground Temperature appearing in Nature, vol. xvii. p. 476, 

 gives me an opportunity of questioning the treatment of the 

 matter and urging the rejection of any figures obtained. This 

 opportunity I had often wished for when reading over the allu- 

 sions to underground temperature which spoil text-books, but 

 would scarcely avail myself of now were not the " report" appa- 

 rently "accepted" in significant silence. 



To any one familiar with the state of circumstances down in 

 mines, who has accumulated thought on the question of 

 the temperature of the rocks in depth, the observations 

 noted in this report must appear, not to say absolutely 

 inadequate to further the inquiry, but altogether missing the 

 point of it — that is to say, if I am right as I take it, 

 that the purpose of the Committee is to ascertain, not mere 

 " underground temperature " readings, but the proper tempera- 

 ture of the rocks as due to intra -terrestrial conditions. In all 

 the obsen-ations conducted in mines, the temperature of the 

 mine ventilation or a temperature almost wholly inter -dependent 

 is expressed by the figures obtained ; these figures no more indi- 

 cate the true state of the case, and are therefore of no more 

 value to the geologist or the general physicist, than the tempera- 

 ture of a greenhouse would assist the meteorologist. The 

 figures obtained in bores express the temperature of the waters 

 standing therein — which temperature cannot at all be assumed to 

 be coincident with the rock temperature ; these figures are de- 

 termined by a variety of factors, the true rock temperature not 



being necessarily the greater. • In fact, wo -can never arriv* at 

 the temperature of the rocks in depth through the media of 

 water or air. To state this truth is to establish it. 

 - A few remarks, however, bearing directly on the details of 

 the observations in the report, may aid inquirers to arrive at a 

 true state of thought on the subject. In the first place, and as 

 of general appHcation, I have to demand attention to the matter 

 of the mine area, to depths exceeding the observation statio'iis^ 

 being depleted of the waters naturally appertaining thereto— 

 and for this reason even a rock temperature ascertained over 

 such an area would be abnormal. A thermometer hung up in 

 a mine way will unquestionably register the temperature 

 of the ventilation in that particular place ; nobody expects any 

 other result. Can the temperature of the ventilation be demon- 

 strated to be inter-dependent in a ^eat measure on the tempera- 

 ture of the surrounding rocks, which is itself abnormal as above 

 submitted ? Certainly not ! and this fact is so obvious to those 

 having a true acquaintance with mine ventilation, that it seems 

 to me too absurd to elaborate proofs of it. Particular stress is 

 laid on the point that currents of air and well-aired situations 

 were avoided. It is hard to see any outcome of this other 

 than still more abnormal readings. Surely observers do not 

 imagine they can penetrate the rocks so far by cornering in 

 mines as to leave the atmosphere wholly behind. Figures 

 obtained in still air express the temperatiu-e of dying ventilation, 

 or of gases of exudation, or partly of both. As to the employ- 

 ment of a few inches of water in a hole, as supposed to secure more 

 direct contact with the rocks, or to isolate from air; the tempe 

 rature of the small body of water so employed is that obtained, 

 and it is obvious it depends on the air temperature, and (worse) 

 the water may possibly be decomposing. These remarks apply, 

 for the most part, alike to the ingenious method employed down 

 Boldon Colliery as to the more simple method of Schemnitz. 

 Then, with regard to the Boldon Colliery observations in 

 particular, the curious in these matters will be led to speculate 

 as to what was going on up the ten-foot hole, and whether the 

 "stagnant " ventilation of the district was not tending towards 

 the explosive conditions. All the circumstances previously set 

 down, supplemented by the exudation of gases, and the sub- 

 sidence of strata following on coal working, combine to render 

 this one of the unhappiest conceivable situations for the research 

 on rock temperature. 



A thermometer down a mine is of no utility beyond qualifying 

 barometric readings. 



The bore observations are, I venture to think, a crude phase 

 of the method which may lead to success ultimately. As hither- 

 to conducted, they are open to many obvious objections, which, 

 if stated at length, would be little more than a reiteration of the 

 above in part. 



I will venture to suggest that the next steps in advance be the 

 permanent placing of instruments in deep bores, broken rock 

 being rammed over as over powder in blasting operations, so 

 that all water and air, except such as may be fairly considered 

 as entering into the structure of the rocks, be entirely excluded, 

 and the application of thermo-electric apparatus devised by 

 specialists in electric science, all constituting a special, and, for 

 many reasons, invaluable attachment to an observatory or 

 kindred institution. WiLLIAM MoRRIS 



Earlshill Colliery, Thm-Ies 



Helmholtz's Vowel Theory and the Phonograph 



The results obtained by Messrs. Jenkin and Ewing in their 

 experiments with the phonograph, as described in Nature, vol, 

 xvii. p. 384, are so different from those reached in some experi- 

 ments recently performed by Dr. Clarence J. Blake, of this city, 

 in connection with myself, that I venture to call attention to the 

 fact. 



With the design of testing the question of change of quality 

 in vowel tones by increasing the rate of rotation of the phono- 

 graph cylinder, we performed a number of experiments, of 

 which I mention a few as briefly as possible. 



I. The vowels on and J were spoken into the mouth-piece of 

 the instrument, each four times in succession, while the cylinder 

 was rotated at the rate of one revolution per second, as timed by 

 the beats of a clock -pendulum. On rotating the disc so as to 

 reproduce the vowel-sounds, these were as spoken, ou, o, each 

 repeated four times, when the rate of rotation was one revolution 

 per second, but on increasing the velocity to two revolutions per 

 second, the first sounds were indistinct, while the last gave the 



