Nov. 8, 1877] 



NATURE 



27 



the United States, of an importation of a real spiritualistic mania, 

 far more injurious to our menial welfare, than that of the 

 Colorado beetle will be to our material interests, I should 

 be untrue to my own convictions of duty if I did not do what in 

 me lies to prevent it. That I do not take an exaggerated view 

 of the danger, will be obvious to any reader of Mr. Home's book. 

 I know too well that I thus expose myself to severe obloquy, 

 which (as I am not peculiarly thick-skinned) will be very un- 

 pleasant to myself, and unfortunately still more so to some who 

 are nearly connected with me. But I am content to brave all, if I 

 can believe that my exposi will be of the least service either to 

 individuals or to society at large. VV. B. Carpenter 



The high scientific position which Prof. Foster holds, as well 

 as the decided manner in which his letter was written, must lead 

 the otherwise unbiassed reader to the conclusion that not only 

 has a satisfactory explanation of the action in question been 

 found and generally adopted, but that this explanation turns 

 upon certain considerations, and particularly on the mean length 

 of the path of the gaseous molecules as influenced by the degree 

 of rarefaction. 



I feel my position, therefore, particularly unfortunate in 

 having, for the sake of truth, to show that the explanation 

 which Prof. Foster has adopted, and supposes others to have 

 adopted, is, if judged by the statements in his letter, inconsistent 

 with well-established laws. 



Prof. Foster gives me credit for having originated the funda- 

 mental idea of the explanation, but states that my "explanation 

 was theoretically incomplete ; in particular it did not show 

 clearly why so high a degree of rarefaction should be necessary 

 for the production of the phenomenon in question ; " and then 

 he proceeds to explain how this asserted deficiency was supplied 

 by other thinkers, who showed that "the increase, resulting 

 from rarefaction, in the mean length of the path of the gaseous 

 molecules, would favour the action." 



It is this supposed completion of my explanation that is 

 erroneous. It is contrary to the law of the diffusion of heat in 

 g3ses ihat "the increase, resulting from rarefaction, in the mean 

 length of the path of the gaseous molecules would favour the 

 action," and so far from supplying any deficiency in my explana- 

 tion it is incompatible with it. The only result from such an 

 increase is to diminish the action — a result which rises into 

 importance only when the rarefaction is carried so far that the 

 mean length of the path of a molecule becomes comparable with 

 the dimensions of the inclosing vessel. 



In my first paper I gave a definite proof, which has nowhere 

 been questioned, that according to the kinetic theory the force 

 arising from the communication of heat from a surface to adjacent 

 gas of any particular kind depends only on one thing, the rate at 

 which heat is communicated, and to this it is proportional. If 

 therefore the increased rarefaction increased the f r -e it must 

 increase the rate at which heat is communicated, but accor^hng 

 to the law established by Prof. Maxwell the rate at which heat 

 is communicated is independent of the density of the gas, whence 

 it follows tbat the increase in the mean length of the path of the 

 gaseous molecules, resulting from rarefaction, cannot favour the 

 action which remains approximately constant until the gas 

 becomes so rare that the law of diffusion no longer holds, alter 

 which it may easily be shown the communication of heat, and 

 hence the action in question, diminishes but never increases. 



The fact that in the radiometer the force caused by the com- 

 munication of heat only causes motion when the surrounding 

 gas becomes extremely rare is, as I pointed out in my first 

 papers, fully explained by the action of what I have called con- 

 vection currents, which action depends on the weight and 

 density of the gas. The gas adjacent to the hot surface is hotter 

 than that which is more remote, and hence the former rises form- 

 ing an ascending column, to supply which the gas is drawn in 

 laterally on all sides, and tends to carry the surface forward 

 with it. With the same difference of temperature and surround- 

 ing circumstances the speed of these convection currents is the 

 same whatever may be the density of the gas, and hence the 

 force which they exert on the surface is proportional to the 

 density of the gas. 



This force is opposite in direction to that arising from the 

 communica ion of heat to the gas, and since the former dimi- 

 nishes with the density while the latter is constant, there must 

 be some density for which they balance, and below which the 

 constant force will predominate, while above this point the con- 

 vection currents will carry the surface with them. The fact that, 



starting from low densities, the motion of the vanes in the radio- 

 meter does not only diminish as the density increases, but is 

 actually reversed at higher densities, requires explanation, and 

 no other than this has yet been offered. 



I have gone into the subject at considerable length, as I felt 

 bound, when venturing to differ from so high an authority as 

 Prof. Foster, to state my reasons. There is, however, nothing in 

 what I have said here which I have not said elsewhere, in the 

 same or other words ; and however incomplete in theory the 

 explanation given in my first papers may be, I can only say that 

 it included all the facts known to me at the time these were 

 written ; it has led me to predict many of the experimental 

 results which have since been obtained, and I have not been 

 able to find one fact with which it is not in accordance, nor has 

 it been, so far as I am aware, controverted in any particular. 



Osborne Reynolds 



Potential Energy 



I HAVE reason to believe that the "grievous error" with 

 which I charged "John O'Toole " in his reference to the clock 

 is not meant by him to be his own view of the matter at all, but 

 merely a legitimate deduction from the confused and inconsistent 

 language of " the doctors." Such an erroneous view on his part 

 is, indeed, obviously out of harmony with the extensive know- 

 ledge of the subject of energy displayed by him in letters which, 

 without doubt, will convince " the doctors " of the necessity of 

 adopting consistent and strictly logical phraseology. 



G. M. MiNCHIN 



Royal Indian Engineering College, Cooper's Hill 



Effects of Urticating Organs of Millepora on the 

 Tongue 



An article by Mr. Moseley, in Nature (vol. xvi. p. 475), 

 reminds me of an experiment I made some years ago in Florida. 

 In collecting corals on the reefs, I had of course become 

 familiar with the disagreeable, though not very painful, effects 

 of contact of the hands with Millepora. But the vulgar names 

 of Pepper-coral or Sea ginger induced me to try the effect on 

 the tongue, to find out how far the taste resembled those condi- 

 ments. I accordingly broke off a fresh piece and applied it to 

 the tongue. Instantly a most severe pain shot, not only through 

 that organ, but also through the jaws and teeth. The whole 

 course of the dental nerves and their ramifications into every 

 single tooth could be distinctly and painfully lelt. I can com- 

 pare the sensation to nothing better than to the application of 

 the poles of a pretty strong galvanic battery. The pain re- 

 mained severe for about half an hour, then became duller, 

 leaving a sensation still perceptible five or six hours later. The 

 whole impression was much too violent to allow the distinction 

 of any particular taste. 



Such an experiment made with Physalia might be positively 

 dangerous, considering the much more powerful urticating effects 

 of its polyps. Indeed, a friend of mine once related to me that 

 when a boy he had come in contact with one of the long tentacles 

 of a Physalia, when bathing, and had to be carried out of the 

 water almost fainting. L. F. Pourtales 



Cambridge, Mass., October 22 



Drowned by a Devil Fish 



The following account of the destruction of a human being by 

 a cuttle fish at Victoria, in Vancouver Island, has all the appear- 

 ance of authenticity about it. It occurs in the Weekly Oregonian 

 of October 6, 1877. The Oregonian is the principal paper of 

 Oregon, and is published at Portland. 



The insertion of the account in Nature may lead to further 

 information on the subject. I know of no other authentic instance 

 of the kind. 



An account of the habits of the huge octopus of the Vancouver 

 Island Sounds and also of the Indian method of hunting and 

 killing the beasts for food is to be found in John Keast Lord's 

 "Naturalist in Vancouver Island and British Columbia," vol. i. 

 p. 192. Mr. Lord measured specimens which had arms five feet 

 in length, with a thickness at their base as great as his wrist, and 

 he once collected a detached sucker of one of these cephalopods 

 as large as an egg cup in mistake for a huge actinia. 



