VOL. XLIV.j PHILOSOPHICAL TRANSACTIONS. 379 



the consequence of which was, that the polypus sticking to the horsetail would 

 be obliged to remain in such a situation, as to be within the reach of a magni- 

 fier that was of a short focus. 



Nothing more was then wanting, but to place the magnifier before the object : 

 for it would be both difficult and very inconvenient to hold it like a reading-glass 

 in the hand. In the instrument k, i, h, g, e, it was screwed into a ring fixed 

 to a small branch n, g, which had a ball g at its other extremity; this ball fitted 

 a socket, and so made a joint, by which the first branch was joined to a second 

 h, i, and that again in like manner to a 3d i, k, or 4th, if there should be oc- 

 casion. The foot of the whole was fitted near the edge, into a small board or 

 tablet that held the whole apparatus. By means of these joints, the magnifier e, 

 mightbe turned anyway, and might be conveniently brought near its proper distance 

 from the object ; yet as the branch which held it, could not well be without some 

 spring, it would be still difficult to adjust the object exactly to the focus of the 

 magnifier when it is short, if only the magnifier was to be moved for that pur- 

 pose; and it was therefore found to be easier, when the magnifier was once right 

 against the object, to move gently the glass in which that was contained, till it 

 should be precisely in the focus of the magnifier: and for this purpose the small 

 board on which the glass was placed, was well smoothed. 



The light that came in at a common window was found sufficient for observ- 

 ing in the water such objects as are to be seen with the bare eye, or with a hand 

 magnifying glass; but such as must be eyamined with a lens of a shorter focus, 

 must be viewed by the light of a taper, placed beyond the glass, and whose flame 

 is to be on the level with the object. 



A magnifier thus once adjusted may remain in the same place before the object, 

 for several days together, without being disordered ; so that, to observe the pro- 

 gress of the insect [animalculum] during all that interval, no more will be neces- 

 sary, than to place from time to time a taper behind the glass, and to apply the 

 eye to the already fixed magnifier. 



Several of these apparatuses may be placed on one and the same board by each 

 other ; and thus at the same time observations may be made and carried on with 

 dififerent sorts of insects, or with several insects of the same species ; in order to 

 come sooner and with more certainty at the knowledge of the facts desired. 



Mr. T. could never have discovered the manner in which the clustering polypi 

 are multiplied, but by the help of the expedient here described : and before he had 

 the use of that apparatus, he only knew in general the figures of those polypi, 

 and of the clusters that contained them. He had taken notice that those clusters 

 grew, and he had reason to suspect, that a whole cluster came from a single 

 polypus; but he still wanted to see this increase, and to find the moment of their 

 multiplication; for he had reason then to suspect, from what he had seen with 



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