RE< i 



the part it goes round npon, and which it must be separate 



.ui<l (liHtin"t II-..IM/ 'I'- tin i . answer that, place the 



in whatever light <>r m . please, when the wheels 



are fully |initni"li"l tiny n.-vi-r fail to show all the visible 



marks im:igiiiul>li.i of a rogulur turning round, which 1 think no 



:. uri'.Mint. !'..r i! tln-y d.i not really do BO. Nay, 



ions yon may with your eye follow the name cogs 



v SIM-HI t . make a complete revolution ; for the 



,' very transparent, they are easily 



ilistiiigiiNh<"l through it. As for the machinery, I shall only 

 nay Hint n. i true judgment can bo formed of the structure and 

 parts of minute insects by imaginary comparisons between them 

 ami larger animal they bear not the least similitude. 



T, as a man can move his arms or his legs circularly aa 

 ..-i he pleases by the articulation of a ball and socket, may 

 in >t there possibly be some sort of articulation in this creature 

 whereby its wheels or funnels are enabled to turn themselves 

 quite round P It is certain all appearances are so much on this 

 side the question, that I never met with any who did not, on 

 seeing it, call it & rotation; though, from a difficulty concern - 



Fig. 1. 





ing how it can be effected, some have imagined they might be 

 deceived. M. Leonwenhoek also declared them to be wheels 

 that turn round. (Vide Philosophical Transactions, No. 295.) 

 But I shall contend with nobody about this matter : it is very 

 easy for me, I know, to be mistaken, and so far possible for 

 others to be so too, that I am persuaded some have mistaken 

 the animal itself, which perhaps they never saw ; whilst, 

 instead thereof, they have been examining one or other of the 

 several water animalcules that are furnished with an apparatus 

 commonly called wheels, though they turn not round, but excite 

 a current by the mere vibration of nbrillto about their edges." 



Notwithstanding the evidence adduced by Mr. Baker, which, 

 as we have said, is admitted by some at the present day, it must 

 be evident, from a consideration of the nature of muscular 

 force and the condition of continuity under which all animals 

 exist, that the rotation cannot really occur. The appearances 

 are altogether so like some of those exhibited in the experiments 

 with cogged wheels, that we feel no doubt the wheels must be con- 

 sidered not as having any real existence, but merely as spectra, 

 produced by parts too minute, or else having too great a 

 velocity, when in use by the animal, to bo themselves recognised. 

 It is not meant that they are produced by toothed or radiated 

 wheels, for that supposition would take for granted what has 



already been considered as impossible continued revolution at 

 one part of an animal whilut another part U Axed ; bat arrange. 

 menU may be conceived which are perfectly oonsuteut with the 

 usual animal organisation, and yet competent to produce all the 

 effect* and appearance* observed. Thus, if that part of the 

 head of the animal were surrounded by fibrilta, endowed each 

 with muscular power, and projecting on all sides, so M to form 

 a kind of wheel ; and if these fibrils were successively moved in 

 a tangential direction rapidly the one way, and more slowly 

 back again, it in evident that currents would be formed in the 

 fluid, of the kind apparently required to bring food to the 

 month of the animal ; and it in also evident that if the fibrils, 

 either alone or grouped many together, had any power of 

 affecting the sight, so as to be visible, they would be lees 

 visible at the part through which they were rapidly moving than 

 that through which they were slowly returning ; and at that 

 place, therefore, an interval would appear, which would seem 

 to travel round the wheel, in consequence of the successive 

 action of the fibrils. But if, instead of the whole group 

 of fibrils acting in succession as one series, they were to be 



divided by the will or powers of the animal into fifteen or 

 sixteen groups, the action being in every respect the same. 

 then there would be the appearance of fifteen or sixteen dark 

 spaces, and as many light ones, disposed as a wheel ; and 

 these would continue to travel round in one direction, so long 

 as the animal continued the alternate action of the fibrils. This 

 may be illustrated by supposing it to represent a fixed circular 

 brush with long hairs, and the little dots to be the sections of 

 so many wires forming the arms of a frame which, when turned 

 round, shall carry the hairs of the brush forward a little, and 

 thei., letting them go, allow them to return quickly to their 

 'first position. If this frame be turned continually round, it 

 would cause the brush, when looked at from a dist<." 

 appear as a revolving toothed wheel, although in reality it had 

 no circular motion. Now, what is performed here by the wire 

 arms at the outer extremity of the hairs, and the natural 

 elasticity of the latter, may in the wheel animalcule be effected 

 at the roots of the fibrillre by muscular power ; and in this or 

 some similar way the animal may have the power of nrginf 

 the current necessary to supply food, and at the same time 

 producing the spectrum of a continually revolving wheel, or 

 even the more complicated forms discovered by Leenwenhoek, 

 without requiring any powers beyond those which are within the 



