378 Philosophical transactions. [anno 1747. 



sorts of these insects, that the simple observation of them in a drop or 1 of 

 water, will not be sufficient to discover all that is singular either in their shape 

 or motion. It is therefore very proper that an observer should endeavour to exa- 

 mine such insects, when they are more at ease, and in a larger quantity of water. 

 And this will be found still more necessary, if we be desirous regularly to pursue 

 their history. For then the same insects ought to be regularly observed, for 

 many days successively, and they ought themselves also to be as nearly as possi- 

 ble under the same circumstances they would have been, had they remained in 

 the same waters in which they naturally live. 



He accustomed himself to keep great numbers of the small insects [animalcula,] 

 on which he made observations in large glasses: and it was by observing what 

 passed in those glasses that he endeavoured to discover the more general facts, 

 relating to the natural history of these animals. After which, he found by many 

 repeated experiments, that it was necessary to remove into glasses of a less size. 

 Tab. 1, such of the insects as were to be set apart for more particular and curi- 

 ous microspical observations. He put water into these glasses, from the same 

 ditches, out of which the insects he was observing had themselves been taken ; 

 and shifted this water more or less often as the circumstances might require. 



To observe a small insect in one of these glasses, with a magnifier of a 

 short focus, the insects [animalcula] should be placed very near to one of the 

 sides of the glass; and it ought also to be kept steadily in the same place. It 

 ought therefore to be either fixed to the side of the glass itself, or to some other 

 body that may be conveniently so fixed. He chose for this purpose, substances 

 that were slender and supple, such as the small branches or twigs of divers spe- 

 cies of the equisetum palustre, or water horsetail. The clustering polypi are 

 often found on these twigs, and they may be made to settle on them from else- 

 where. 



Now this is the method he took, to fix one of these twigs of horsetail against 

 the side of his glass. Having chosen a small slip, on which there was one or 

 more of the clustering polypi he took a piece of a peacock's feather, from which 

 he cut away all the beards on both sides, excepting one at the extremity; on this 

 one he made a knot near its insertion, but did not at first draw it close. He then 

 brought this open knot to the small slip of the horsetail that was floating in the 

 water of the glass, and getting one of its extremities into the knot, he then drew 

 it close; and thus the slip of the horsetail is joined to the piece of the feather. 

 He next took hold of the feather, and bending it near the middle, he forced its 

 1 endsb, f, fig 7, pi- 8, into the glass; he then let go the feather which he 

 before held, and its elasticity would force its 1 ends against the sides of the glass 

 A, by which means the small twig d 1 of the horsetail, which was already fixed to 

 the extremity of the feather f d, would become also fixed to the side of the glass; 



