380 PHILOSOPHICAL TllANSACTlONS. [aNNO 1747. 



a glass held in his hand, that these clusters did not grow insensibly like plants ; 

 but that on the contrary, the operation was performed in a short portion of time. 

 He therefore resolved to observe regularly for some time polypi of this kind with 

 his microscope, while they should remain in circumstances, nearly as easy and as 

 natural to them, as those they were in in their proper habitation. 



This gave him the first thought of the above-described apparatus. And when 

 he had prepared and fixed every thing, he set himself continually to watch for 

 the moment of the mviltiplication of the clustering polypi; and he then found 

 this moment, which he had so much wished to discover, the very same morning 

 that he began to make use of his apparatus. 



It was, as has been seen in the paper above referred to, in that species of 

 polypi, some of which are represented in the 1st, 2d, and 3d figures of the 2d 

 plate of this Vol. Q, that he first discovered the manner in which these small 

 animals are multiplied. It is also in the same species easy to see that very odd 

 motion, which they exhibit at their anterior extremity. This same motion, 

 which has also place in other species of clustering polypi, is not in them so easy 

 to be remarked; both because they are smaller, and also as this motion itself is 

 swifter, than in the sort above-mentioned. 



There is also to be observed at the anterior extremity of several other small 

 insects, a sort of motion which has drawn the attention of all such as have 

 happened to see it, and who have almost all been curious to inquire and satisfy 

 themselves, whether those little wheels, which appear to turn with so swift and 

 so regular a motion, are really wheels turning on an axis or not. This deter- 

 mined him now to mention that motion, though it is not his design to treat fully 

 of it in this place, or to determine very precisely what he thought about it: as 

 he would be very cautious how he asserted any thing positively on so nice a matter, 

 till he should have repeated several experiments he had then made. 



In order to discover what this motion might really be, he applied himself not 

 only to observe it in the same animal placed in different altitudes, but also in dif 

 ferent species of water-insects [animalcula] in which it is seen, and he has com- 

 pared the phenomena of all these several motions one with another. These 

 comparisons he has found in other cases to be of singular use, and the best 

 means of preserving himself from those illusions, which very small objects, 

 viewed in a microscope, especially while they are in motion, are but too apt to 

 present. 



All he had then learned from these comparisons, and all the other observations 

 he had made, seemed to prove that there is some deception of the sight in the 

 present case, and that the motion in question is not really what it at the first 

 appears to be, a rotatory motion round an axis. And he knew some species of 

 polypi, in which this motion is, comparatively speaking, but slow: and in these 



