NATURE 



\ytine 13, 1872 



On Adhesion Figures 



A DROP of crude carbolic acid placed on the surface of cold 

 water exhibits the most sur|)rising and beautiful " cohesion 

 figures." I am not a.vare tliat Mr. 'fomlinson has described the 

 behaviour of tliis substance. So lively and unpredicted arc the 

 movements of the dro]i that its action resembles that of a living 

 creature. At first it pulsates, then its edge breaks up into crispa- 

 t ions, and a motion begins like the waving tentacles of a sea- 

 anemone. Sometimes the drop will siil about in a crescent 

 shape, or .shoot out independent little rings, which gyrate and 

 rush about like a rotifer, until at last they burst into a myriad 

 of intensely active little specks. Warm water destroys all action, 

 by lessening, I suppose, the adhe~.ion of the liquids. 



To your readers it is trite and useless to remark upon the 

 interest that attaches to the careful and continued observation of 

 the most familiar things. But I wish the leisure classes could 

 understand this. How many pleasant and instructive hours 

 might some of them spend in examining such common things as 

 essential oil dropped on water, even drops of ink falling through 

 water, or puffs of smoke through air or a candle llame, or a 

 hydrogen flame, or iron filings sprinkled on paper over a magnet, 

 or, among other simple things, best of all a block of ice in a sim- 

 beam. From the contemplation of such phenomena one rises 

 with an increasing joy, and not a little humbled at one's own 

 ignorance before the orderly mystery that pervades everything. 



24, Elgin Road, W. J. H. Spalding 



A Suggestion to Opticians 



There is a method of mounting self-registering meteorological 

 thermometers very commonly employed, and one which for 

 some purposes, as, for instance, for determining the temperature 

 immediately over the surface of the ground, is an excellent 

 plan. 



I allude to the placing of the divided thermometer stem in a 

 larger tube forming a jacket to it, and fixing it with india-rubber 

 packing, which makes an air-tight stopper round the neck. 



Now it is frequently observed that when thermometers fitted in 

 this manner are exposed to cold, a copious deposition of dew 

 takes place, both on the stem and in the interior of the jacket, 

 rendeting the accurate reading of the instrument a matter of 

 some difficulty. I would therefore suggest to makers of ihis 

 class of instrument whether it would not be advisable for them 

 to dry, I do not mean merely heat, the air in the tubes, or else 

 enclose some water-absorbing substance, as calcium-chloride, in 

 the tube before finally inserting the indii-rubbcr stopper. 



It is extremely probable my suggestion is not a new one. I 

 have no recollection, however, of having heard of such a plan 

 being employed by any maker. G. M.\thus Whipple 



Kew Observatory, June 10 



The Ferrara Floods 



May I ask for space to draw the attention of engineers to the 

 question whether the beds of embanked livers rise or not ? The 

 affirmative is argued (and in reference to Ferrara) in the last 

 chapter of "Rain and Rivers," against the negative of the 

 eminent American engineer EUet. The title of the chapter is 

 " EUet on the Mississippi." George Greenwood 



Brookwood Park, Alresford, June 8 



FORCE AND ENERGY 



THE CONSERVATION OF ENERGY A FACT, NOT 

 HERESY OF SCIENCE 



IN an article entitled " The Heresies of Science," pub- 

 lished in a recent number of the London Quarterly 

 Rcvicio, two widely different principles are oddly linked 

 tof'ether as heretical dogmas, the doctrine of Evolution, 

 and the Conservation of Energy. 



On the doctrine of Evolution the writer has nothing to 

 say. 



Be fo e discussing with the " Reviewer " the validity of 

 the Conservation of Energy, it is quite necessary to 

 define the terms which may'be employed, such as Force, 

 Energy, Potential, Sound, Light, Heat. 



It is much to be regretted that a far greater degree of 

 logical accuracy in the use of terms than is usually met 

 with, does not exist amongst even the ablest writers on 

 physics, for many of the arguments adduced against 

 physical principles lie not against the principles them- 

 selves, but against the indefinite language in which they 

 have from time to time been expressed. There is probably 

 no term employed in physics that has been more misap- 

 plied, and in its misuse has led to greater confusion of 

 ideas, than " force." 



Force has been thus defined by our ablest modern 

 physicist.* "What I mean by the word force is the 

 source or sources of all possible actions of the particles or 

 materials of the universe." 



This definition of force is substantially the same as the 

 writer's definition f to which the reviewer takes exception, 

 but which may perhaps with advantage be thus amplified : 

 Force is a mutual action between the atoms or mole- 

 cules of matter, by which they are either attracted towards, 

 or repelled from, each other ; and by this action energy is 

 imparted to the matter put in motion. It may be further 

 remarked that force is essentially either attractive or 

 repulsive. 



The writer sees no reason to amend his definition of 

 " Energy" — namely, that it is ilic power of doing work. 

 It may, however, be remarked that the existence of energy 

 in matter implies the existence of motion, and vice versd; 

 but it by no means follows that motion and energy are 

 convertible terms, for motion means only the act of 

 moving, or changing the position occupied in space. 



The term " Potential " applied to force or energy means 

 inactive, but capable of being called into action. Thus, 

 if a weight be raised, a certain amount of energy is ex- 

 pended in raising it, and so long as the body is supported 

 the energy expended in raising it remains potential in it, 

 but when allowed to fall freely in vacuo to the level from 

 which it was raised, the body acquires exactly the amount 

 of energy that was expended in raising it. In the same 

 manner the repulsive force of the molecules of the highly 

 ignited gases into which gunpowder is resolved by igni- 

 tion may with equal propriety be said to be potential in 

 the unignited powder. 



The remarks with which the writer's interpretation of 

 the terms " force " and " energy " have been met by 

 the reviewer may here be appropriately noticed. 

 Quoting the introductory chapter already referred to, he 

 adds : " his doctrine regarding the nature of force has 

 thus no connection with sound philosophy ; by force Mr. 

 Brooke evidently means what other advocates of con- 

 servation mean by potential energy." Does then sound 

 philosophy consist in the impossible task of agreeing as 

 to the meaning of terms with those who do not agree 

 amongst themselves ? Or is sound philosophy monopo- 

 lised by, and crystallised in the opinions of the reviewer ? 

 Sound philosophy would seem to consist rather in assign- 

 ing appropriate meanings, involving no inconsistency or 

 contradiction, to terms of frequent occurrence in all works 

 on physics. 



If the above definitions of force and energy be accepted, 

 it is obvious that the term " force," as used by Grove, 

 Tyndall, and many others, means sometimes force and 

 sometimes energy. Thus, for example, " the conservation 

 of force " becomes a simple truism, for its exercise being 

 a function of matter, force must necessarily be coeval 

 with matter. The reviewer (p. 22) thus quaintly expresses 

 the relations of force, energy, and motion: — "A given 

 motion viewed as a cause is force, while the very same 

 motion thought as an effect is energy." Motion, it is 

 presumed, can mean nothing else than the act of moving ; 

 but how the act of moving, whichever way we look at or 



^ F.iraday, MSS. Croonian Lectures on Matter and Force, by H. Bence 

 Jones, M.D. p. 35- 



t Introductory chapter to the Sixth Edition of "The Elements of 

 Natural Philosophy." 



