is only apparent in those drops that are flattened, in consequence of being nearly or absolutely in contact with the stage of the microscope.
That the motion of the particles is not produced by any cause acting on the surface of the drop, may be proved by an inversion of the experiment; for by mixing a very small proportion of oil with the water containing the particles, microscopic drops of oil of extreme minuteness, some of them not exceeding in size the particles themselves, will be found on the surface of the drop of water, and nearly or altogether at rest; while the particles in the centre or towards the bottom of the drop continue to move with their usual degree of activity.
By means of the contrivance now described for reducing the size and prolonging the existence of the drops containing the particles, which, simple as it is, did not till very lately occur to me, a greater command of the subject is obtained, sufficient perhaps to enable us to ascertain the real cause of the motions in question.
Of the few experiments which I have made since this manner of observing was adopted, some appear to me so curious, that I do not venture to state them until they are [5 verified by frequent and careful repetition.
I shall conclude these supplementary remarks to my former Observations, by noticing the degree in which I consider those observations to have been anticipated.
That molecular was sometimes confounded with animalcular motion by several of the earlier microscopical observers, appears extremely probable from various passages in the writings of Leeuwenhoek, as well as from a very interesting Paper by Stephen Gray, published in the 19th volume of the Philosophical Transactions.
Needham also, and Buffon, with whom the hypothesis of organic particles originated, seem to have not unfrquently fallen into the same mistake. And I am inclined to believe that Spallanzani, notwithstanding one of his statements respecting them, has under the head of Anima-
