344 



♦ KNOWLEDGE * 



[April 24, 1885. 



The second condition of easy action is smoothness or con- 

 tinuity. A rapid succession of stoppages and renewals in 

 the activity of any organ, caused by the quick withdrawal 

 and return of its appropriate stimulus, is unpleasant, 

 because the organ is constantly trying to acoommoddte 

 itself to altered circumstances, and never has time allowed 

 it for complete fruition. This second condition should be 

 carefully remembered, because it is the basis of some of my 

 future arguments.* 



We can now see that the love for light and colour is 

 not a product of natural selection, though without natural 

 selection it could not have been perpetuated. The first 

 animal which developed a dim colour-perception would from 

 the outset find pleasure in exercising the new faculty. As 

 the animal grew and throve, the multifarious stimuli con- 

 veyed to it Irom the external world would incline it to free 

 exercise of all its parts ; and any slightly excessive exercise 

 of the dawning .sense would bring a larger supply of nutri- 

 ment to the new and as yet unstable organ, tending to 

 improve and to diversify its structure, and to make it better 

 able, and therefore more i-eady, to [)erform and to vary its 

 functions. Increase in efficiency would mean increase of plea- 

 sure, and the pleasure, by inducing greater exertion, would in 

 its turn promote efficiency. Such evolution could, of course, 

 not take place (at least in these early stages) unless the added 

 .sense were more or less serviceable to the organism. But 

 manifestations similar to those which we associate with the 

 pleasures of vivid sensation are observed in some creatures 

 which we can scarcely credit with consciousness. The 

 objective — that is, the physical — side of the process is 

 present; but the subjective — that is, the mental — has yet 

 to be developed. Mr. Romanes! tells us that the tiny 

 Englena Viridis — a mere speck of jelly — " definitely seeks 

 the light It prefers the blue rays [probably because, for 

 some unknown reason, they act upon it more strongly than 

 the other rays of the spectrum]. A colourless and trans- 

 parent area of protoplasm iu the interior part of its body 

 is the most sensitive." Actual organs of sight first occur 

 in the medusae, which " seek the light folio wing a lantern 

 moved round a bell-jar containing them in a dark room," 

 while " starfish and eclimi crawl towards and remain in 

 the light, even though of such feeble intensity as scarcely 

 to be perceptible to human eyes." Yet, whatever may be 

 said of meduspe and starfish, it is difficult to credit our 

 little Englena with what is usually called sensation. 



Here, then, we have to state our law a little differently, 

 substituting "well-being" for "pleasure," and "waste" 

 for " fatigue." The greatest well-being is derived from the 

 maximum of activity with the minimum of waste. The 

 vigorous discharge of any function, when n )t carried to 

 great excess, reacts beneficially on the organism as a whole. 

 Therefore, those organisms which court varied stimulation 

 are the most likely, other things being equal, to survive 

 and to replenish the earth. 



As we ascend in the scale of existence, consciousness 

 emerges, and this well-beiug is translated into its subjective 

 correlate — pleasure. Flies and mollis even commit suicide 

 from sheer love of light. Bees, as we have seen, are 

 mercenary in their fondness for colours ; but this cupboard- 

 lovo is probably mingled with a purer passion. Sir J. 

 Lubbock finds that they chiefly afi'dct orange and yellow, 

 and that they like blue next best. It is in birds, however, 

 that we have the first trace of something like human 

 nestheticism. 



{To he continued.) 



* It is, indeed, tlio chief poiut ia which my theory differs from 

 that of Mr. Allen. 



t " Mental Evolation in Animals." .. ;;- 



THE YOUNG BLBCTRIOIAN. 



By W. Slingo. 



(Coniinued from p. 303.) 

 TAPPING. 



EX. XLIX. — One of the most essential, and withal one 

 of the simplest, processe.s iu the manipulation of 

 tools is that of "tapping " or preparing a female or internal 

 thread into which a screw is to be driven. In order to 

 tap successfully, attention to a few precautions, insignifi- 

 cant as they may at first sight appear, is absolutely 

 necessary. 



In the first place a hole must be bored by means of a drill 

 (Ex. XXIX., kc.) in the piece of metal to be tapped, the 

 size of the hole being equal to that of the tap at the bottom 

 of the thread ; that is to say, if the tap were deprived of its 

 threads, the remaining piece of wire should just pass into 

 or through the hole. This is most important, as, if the 

 hole is too small, the tap, in forcing its way through, has 

 to remove more metal than would be involved in simply 

 cutting the thread. The consequence of throwing such 

 work upon the tap is frequently a fracture, due to the 

 torsion exerted. On the other hand, if the hole is made 

 too large, there is not sufficient metal to give a fully-formed 

 thread. 



The hole being duly made, proceed to tap it. Hold the 

 tap firmly between the jaws of a hand-vice (Ex. XXVIII.) 

 (the tap being provided with a flat end for that purpose), 

 and screw it gently and carefully into the hole. As in 

 making the tap, so in using it to tap a hole, the tool should 

 be turned only so long as it progresses with a moderate 

 degree of freedom. When resistance to the forward 

 motion is experienced, the tap should be turned backwards 

 slightly to relieve the strain exerted upon it, and the 

 forward movement then repeated, this being continued until 

 the entire thread is produced. It is imperative that the 

 axis of the tap should correspond with the axis of the hole. 

 The result of failing to secure this is that, supposing a flat- 

 headed screw to be subsequently driven into the hole, it 

 will not go right home, one side only of the head being 

 able to come into contact with the metal. 



So far as concerns the fixing of the work to be tapped, 

 it may be secured in the table- vice (Ex. XXVI.), but it will 

 often be found preferable to hold it in the left hand, the 

 taj) being worked with the right hand. 



When tapping a deep hole bored only a part of the way 

 through a piece of metal, the tap should bo removed 

 occasionally, and such cuttings as ma}' be in the hole 

 removed. Care is necessary to avoid driving the tap too 

 far into such a hole ; it should never be allowed to jamb 

 against the bottom of the hole, or it will stand a good 

 chance of being broken, and that would not be the worst 

 part of the mischief, for the lower portion of the tool 

 would be left in the hole and the work probably spoiled. 



A HOME-MADE SCREW-PLATE. 



Beginners often experience considerable inconvenience, 

 or, rather, annoyance, in using the screw-plate for the pre- 

 paration of screws. This want of practice often results in 

 the breakage of a screw under manufacture in the screw- 

 plate, whereby the plate is more often than not rendered 

 subsequently useless so far as that hole is concerned. At 

 the best, such a trouble must seriously injure the plate. It 

 is advisable, therefore, the taps having been once made, to 

 use the plate as a standard, and with the taps to prepare 

 other plates for general use. 



Ex. L. — A simple form of home made screw-plate is 



