March 17, 1881] 



NATURE 



463 



the peculiar state of matter observed by Mr. Crookes does 

 not depend on the rarefaction of the gas, but on the 

 dimensions of the bulb (or confining envelope) relatively 

 to the mean path — inasmuch as if it were possible to 

 construct a bulb approximating to the mean path of 

 the molecules of gas at (or near) normal density, ana- 

 logous phenomena would inevitably occur, though of 

 course they could not be observed by very small dimen- 

 sions. [Besides the electric discharge cannot so readily 

 take place in dense gas.] What is done therefore is to 

 raise the mean path appro.^iimately up to the diameter of 

 the bulb (by a high degree of rarefaction\ instead of — 

 conversely — diminishing the bulb down to the length of 

 mean path (at a lower degree of rarefaction) ; when the 

 effect would be difficult to perceive from the smallness of 

 scale. It will be observed that it is only a question of scale 

 (rarefaction being a mere relative thing) — only it becomes 

 possible to use a bulb or containing vessel of larger size (to 

 produce the conditions) in direct proportion as the rare- 

 faction is greater ; so that the whole effect becomes more 

 magnified and distinct. The truth of this view may be 

 more apparent by considering the case of the atmosphere 

 when, at different heights, different degrees of rarefaction 

 prevail Let us take the heights where the mean path of 

 the molecules is (say) one-tenth of an inch, one inch, and 

 ten inches respectively. Then at all these heights (as at 

 ordinary density) the molecules of the gas move in the 

 same normal "radiant" manner, or there is nothing 

 peculiar about the state of the gas at any degree of rare- 

 faction. If now a portion of gas be inclosed at each of 

 these heights in bulbs of one-tenth of an inch, one inch, 

 and ten inches in diameter respectively : then the gas in 

 all these bulbs will be in an abnormal condition, or in that 

 peculiar state where it has ceased to have the power of 

 adjusting its pressure, and consequently the phenomena 

 of diverting the molecules (by suitable means, electric, &c.) 

 into any paths at desire will be possible in all the bulbs. 

 These considerations will perhaps contribute something 

 towards clearing up any difficulties or divergence of views 

 as to the theoretic aspects of this question — which happens 

 to trench on a line of inquiry pursued by the present writer 

 for some years. Returning to our former example, it may 

 be instructive to consider what takes place on further 

 rarefying. Suppose the rarefaction to be carried to 

 another millionth, by opening out our cubical room into 

 another whose linear side is loo times greater, viz., 10,000 

 feet. Here the mean distance of the molecules becomes 

 one seven-hundredth of an inch (multiplying by a hundred) 

 — still a very small quantity, it will be observed. It maybe 

 remarked that by this degree of rarefaction (about a million 

 times further than a good mercurial pump could attain) 

 there are still no less than 340 million molecules in each 

 cubic inch of the space. The mean path however has 

 now sprung to sixty miles — greater than the dimensions 

 . of the room (by about twenty to thirty tines).' Our room 

 has therefore approached the state of a confined bulb 

 where the molecules of gas have lost control over them- 

 selves, or cannot adjust their motions so as to move in a 

 "radiant" manner, but the molecules rebound irregularly 

 backwards and forwards from one wall to the other, 

 without (as a rule) colliding together, and may produce 

 considerable irregularities of pressure. In order to 

 restore the uniformity of pressure, and reproduce the 

 normal " radiant " form of motion, it would be necessary 

 to open out our room into another a considerable multiple 

 of sixty miles in the side (the mean path)— adding fresh 

 gas so as to leave the density unchanged. Here we 

 should have molecules moving in streams and passing 

 ■within (on an average) one seven-hundredth of an inch of 

 each other, and "radiating " from each point of the room 

 with perfect symmetry to a distance of many miles, like 



' It evidently follows from these considerations that if it were possible by 

 some practical means to e-xpand a glass bulb after rarefying : the mean paT\i 

 of the molecules of the inclosed gas would increase three limes as faft as t*i» 

 pismeter of the bulb. 



the rays of light from a luminous point. In tliis case we 

 should have molecules capable of becoming virtual 

 carriers of energy to radial distances such as might really 

 in principle serve to some extent the practical object 

 required in the case of light. 



If we imagine (for further illustration) the rarefaction 

 carried a million times beyond this — viz., to a millionth X 

 a millionth X a millionth of an atmosphere — then the 

 mean distance of the molecules would still only have 

 risen to the small amount of one-seventh of an inch ; but 

 the mean length of path sixty million miles (about). We 

 are thus approaching astronomical distances. It seems 

 a curious fact to consider that a portion of matter can be 

 projected among other portions only one-seventh of an 

 inch apart, so as to move (on the average) sixty million 

 miles without touching one of them. This may form an 

 illustration of the smallness of molecules. A hydrogen 

 molecule moving at about four times the velocity of a 

 cannon ball (its normal rate) would take, calculably, 

 about a year and three quarters to traverse its mean path 

 under these conditions. 



These considerations may serve to show, or facilitate the 

 conceptions as to how particles of matter may have 

 an extremely small mean distance and yet have an 

 extremely long mean path. For it is readily con- 

 ceivable that since (as has been mathematically proved 

 by Clausius and others) the mean length of path of 

 a particle increases, cceteris paribus, as the square of 

 its diameter diminishes (a rapid rate) — particles, such as 

 those of the tether, for instance, may have such an 

 adequately small diameter as to admit of being in \ery 

 close proximity, and yet their mean path extremely 

 great (many millions of miles long perhaps). These con- 

 clusions, rendered more interesting by the additional 

 light thrown on streams of molecules in the gaseous 

 state by the experimental researches of Mr. Crookes — 

 would therefore point, in their possible application to the 

 sether, to a possible means for carrying energy in a 

 "radiant" manner, producing gravity (or the general 

 phenomena of approach), and capable of serving as a 

 great source of motion, the transferences of which are 

 illustrated and exemplified in the motions developed in 

 gross matter on every hand, and which to the appreciative 

 mind who will not admit \^i^ creation of motion, inevitably 

 demand the presence of an agent inclosing a hidden store 

 of motion. The above view would also have the advan- 

 tage of correlating the Kther with ordinary matter (as 

 merely a body consisting of very much finer molecules — 

 or a difference of scale). Why should we suppose the 

 aether to be something abnormal or different from ordi- 

 nary matter, without positive evidence ? Would not this 

 be a deviation from the rule of admitting one principle as 

 sufticient until two are found to be necessary ? This also 

 holds in regard to energy. Why countenance at all two 

 kinds of energy until we have evidence, or why deviate 

 from one grand fundamental principle until we are forced 

 to do so- hardly a probable event, especially when this 

 deviation involves something like a rush into the incon- 

 ceivable represented by an energy ivitJiout motion ? ' 



In conclusion it should be observed that there is 

 nothing hypothetical in the above deductive results re- 



■ The apparently logical plan of admitting one principle until tmo are 

 shown to be necessary would appear to be reversed in the case of energy. 

 It would seem that two kinds of energy are first believed m, because the 

 existence of one kind is not (as it is said) physically proved yet-; .-. proved 

 in such a way as to be obvious to our gross senses, and not merely a deduc- 

 tion derived from pure reasoning based on the observed and otherwise inex- 

 Dlicable developments of motion taking place in gross matter everywhere 

 around us. Some might think that the contrary procedure to the above 

 would be the more logfcal -viz. . to believe in one kind of energy, became the 

 existence of two kinds had not been prcn'ed yet. But in the history of scieiice 

 there has nJtoriously always been a tendency to lean towards the inconceiv- 

 able rather than be contenled with what our understanding can teach us. 

 At a' future day possibly the recognition that all energy is of one character 

 will be thought by some a grand discovery. Some may h .w-ever think it to 

 be only the correction of an err jr which ought never to have been com- 

 mitted for which there was nj real justification-all aiialogy, rat.onality of 

 concepti .-a. and that oneness of principle so characteristic of nature pointing 

 the othei vay. 



