[ 6 35 ] 
to be remarked 5 both on account that they are 
leffer, and alfo on account that this motion itfelf is 
fwifter, than in the fort above-mentioned. 
There is alio to be obferved at the anterior ex- 
tremity of feveral other fmall infeds, a fort of mo- 
tion which has drawn the attention of all fuch as 
have happen'd to fee it, and who have a I mod all 
been curious to enquire and fatisfie themfeives, whe- 
ther thoie little wheels, which appear to turn with 
fo fwift and fo regular a motion, are really wheels 
turning upon an axis or not. This has determined 
me now to mention that motion, tho it is not my 
defign to treat fully of it in this place, or to deter- 
mine very pi^ecifely what I think about it : as I fhall 
be very cautious how I aflert any thing pofitively 
upon fo nice a matter, until I fhall have repeated 
again feveral experiments I have already made, and 
until I fhall have tried feveral others. 
In order to difcover what this motion might 
really be, I have applied myfelf not only to obferve 
it in the fame animal placed in different altitudes, 
but alfo in different fpecies of water-infe&s in which 
it is fecrn, and I have compared the ‘Phenomena of 
all thefe feveral motions one with another. Thefe 
comparifons I have found in other cafes to be of 
lingular ufe, and the beft means of preferving my- 
felf from thofe illufio.ns, which very fmall objects, 
view’d in a microfcope, efpecially whilfl they are in 
motion, are but too apt to prefent. 
All I have yet learned from thefe comparifons, 
and all the other obfervations I have made, feem 
to concur in proving to me, that there is fome 
deception of the fight in the prefent cafe, and that 
the 
