196 



♦ KNOW^LEDGE ♦ 



[July 1, 1887. 



feet apart, were carrietl simultaneously in opioosite direc- 

 tions. Sometimes two or more piece-> went round in circles ; 

 at others, two of tlie biggest hopped rapidly about each 

 other like lively birds at play, but none rose many feet from 

 the ground. It frequently happened that the velocities of 

 their movements varied considerably beyond what could 

 have resulted from impacts of air-currents of the same force 

 upon objects diflering slightly in size, weight, and shape. 

 It was plain that the wind moved in narrow streams, vary- 

 ing in velocity, so that objects a few feet apart received 

 blows of very did'erent force. 



I cannot remember distinctly enough for exact reference 

 where I saw an account of experiments which illustrated 

 this behaviour of a wind-storm. So far as I can recollect, 

 screens of small dimensions were placed in line, and so 

 arranged as to record the force of the wind impact. The 

 result showed that the air-curi-ents struck the screens much 

 as if a quantity of balls, big and little, had been hurled at 

 them. 



Storms of very limited breadth are known to be of 

 common occurrence, and while disastrous damage has been 

 done to trees and buildings within a few yards of each other, 

 adjacent objects have had no .strain put upon them. What 

 the wind at Babbicombe did was to imitate over and over 

 again this sort of action on a minute scale. 



Probably in all violent cyclones it is a mere chance whether 

 any of the usual anemometers happen to receive and indicate 

 the extreme force with which some part of a much larger 

 object would be struck. Some years ago a storm of small 

 breadth in its most violent part overthrew my observatory, 

 made of wood strengthened with T iron and covered with 

 stout canvas, while no damage was done to trees a few yards 

 off. An anemometer near the trees would not have indi- 

 cated anything like the force which lifted up and cariied 

 forward the observatory. 



It would be well worth while to erect in some situation 

 exposed to storm-winds a screen representing a section of a 

 house or bridge, and arranged like the one mentioned, in 

 registering comjiartments. We might thus obtain a better 

 idea of the forms and the forces of wind currents, and of the 

 resisting power requii'ed for safety. 



FORCE AND ENERGY. 



ALTHOUGH so frequently used by scientific 

 and unscientific writers, the words " force " 

 and " energy " are constantly confounded. 

 I find many misinterpreting, on this account, 

 passages in which the words are used. It 

 may, theiefore, be worth while to indicate 

 the sense in which these words are to be 

 understood in accordance with the meanings now definitely 

 assigned to them in scientific writing. They should, in 

 reality, be no more confounded as thus used than gravity 

 and heat — gravity is, indeed, a form of force, and heat a form 

 of energy. Force is any cause by which motion is produced 

 or modified. A force in thus moving or modifying motion 

 does work. The work stored up, as it were, in a body, 

 through the action of a force upon it, is called enen/i/. If I 

 throw a stone into the air I exert force upon it ; the velocity 

 I communicate to it lepresents the work done upon it, and 

 this velocity possessed by the body, at the moment when it 

 leaves my hand, lopresents the energy of the mass which, 

 before I threw it, had been inert. The energy possessed by 

 the body may seem to vary, and actually does vary, but not 

 quite so much as it appears to. It varies because owing 

 to the resistance of the air the enei'gy of the body is 

 continually being diminished ; but the energy thus lost by 



the body is transmitted to the air. But the further loss of 

 velocity on account of the earth's attraction retarding the 

 velocity of the body which had originally been thrown 

 upwai'ds, is not a loss of energy, for the change of place 

 involves a corresponding increase of what may be called 

 energy of position, and this velocity will be presently 

 restored as the attraction of the earth draws the stone down 

 again. In imparting velocity to the stone, again, I was not 

 inci-easing the stock of energy in the universe ; for by what- 

 ever ujjward action I drove the stone from the earth, I 

 correspondingly (regard being had to the relative mass) 

 urged my own body towards the earth, depriving my body of 

 just as much energy of position as corresponded with the 

 energy I imparted to the stone. Energy is, in fact, akin in 

 one respect to mass — it may be taken from or imparted to 

 a body, or from a system, or imparted thereto ; but its 

 totality can never be altered, any more than the total amount 

 of matter in the universe can be altered. 



It has been stated that with regard to these words 

 " force " and " energy " science has no settled usage, but 

 there is no foundation whatever for this statement. The use of 

 the words has long been definitely fixed in scientific treatises. 

 Those unfamiliar with mathematical and physical science 

 are very apt to misuse both words, as also to substitute for 

 one or other words which have no such definite scientific use 

 — as power, might, influence, and so forth. But ahiisus noii 

 lollit usum, the abuse of anything, as Guy Mannering puts 

 it, doth not abrogate the lawful use thereof. 



Probably the confusion wliich has arisen among outsiders 

 respecting these two words " force " and " energy " has been 

 caused in great part by the varying inter-relations of force 

 and energy as cause and ell'ect at one time, effect and cause at 

 another, though, indeed, one ought rather to say that they 

 appear at one time as following and antecedent, at another as 

 antecedent and following, respectively. Yet, in reality, we 

 must regard energy as the true antecedent, seeing that in its 

 fullest sense energy is (as defined by Rankine) the capacity 

 to effect changes. When force is exerted, energy, as we 

 have said above, is stored up somewhere in precise propor- 

 tion to the exerted force : but that force was itself the 

 jjroduct of pre-existing eneigy. Nor do we ever recognise 

 force which has not in some way been generated by the 

 exertion of some form of energy, though, as in the case of 

 the attiaction of gravity, we may be unable to say what 

 that form of energy was, or how it may have been exerted. 



Doubting Faith. — Of old it was held to be a dangerous 

 thing to inquire too closely into the nature and origin of the 

 earth on which we live. Men might inquire, though only 

 with caution, into the natural processes taking place around 

 them ; into the growth of plants and animals ; or into the 

 origin of winds, rivers, and other such phenomena. It was 

 not held, for example, to be an obvious sign of Atheistic 

 tendencies to di.scuss the development of a tree from the 

 seed, or to trace the progi-ess of a river from its source. 

 But a warning voice was heard .so soon as inquiries were 

 pushed a little farther. If observant men, for instance, 

 were led to examine the formation of a river-valley, and 

 thence to inquire under what forces that valley had assumed 

 its present form, they were told that they were pushing 

 their queries Ijeyond the verge of what man was suflered to 

 understand. Worthy people in those days seem to have 

 laboured under a continual fear of discovering too much, of 

 coming unexpectedly upon the operation of a first cause. 

 They seem to have felt that as Mo.ses took off his .shoes 

 when he ajiproached the bush, so it behoved them to proceed 

 cautiously and as with unshod feet, lest unwarily they 

 should light on evidence of the direct action of the Creiitor's 

 fashioning hand. 



