128 LT. 8. Hunt—Celestial Chemistry. 
subsequent to the publication of the first edition of the Prénez- 
pia. The Latin translation of the Optics, by Dr. Clarke, which 
was published in 1706, and the second English edition, in 1718, 
contain successive additions to these queries, which are indi- 
cated in the notes to Horsiley’s edition of the works of New- 
ton, and are important in this connection. From a collation of 
all these, we learn how the conceptions of the Hypothesis took 
shape, were re-inforced, and in great part incorporated in the 
Principia. 
In the Hypothesis, he imagines ‘an etherial medium much 
of the same constitution with air, but far rarer, subtier, and 
more elastic.” “ But it is not to be supposed that this medium 
is one uniform matter, but composed partly of the main phleg- 
matic body of ether, partly of other various etherial spirits, 
much after the manner that air is compounded of the phleg- 
matic body of air intermixed with various vapors and exhala- 
tions.” Newton further suggests in his Hypothesis that this 
complex spirit or ether, which, by its elasticity, is extended 
throughout all space, is in continual movement and interchange. 
“For nature is a perpetual circulatory worker, generating fluids 
out of solids, and solids out of fluids, fixed things out of vola- 
tile, and volatile out of fixed, subtile out of gross, and gross out 
the sun and planets. 
The language of this last sentence, in which his late biogra- 
pher, Sir David Brewster, regards Newton as “amusing lf 
with the extravagance of his speculations,” at which “ we may 
be allowed to smile,”* was not apparently regarded as unrea- 
sonable by its author when, more than ten years later, he quote 
it in the postscript of his letter to Halley, dated Cambridge, 
June 20, 1686. The views therein contained, with the single 
exception of the suggestion regarding gravitation, have not 
wanted advocates in our own time, and many of them were 
embodied in the Principia, which Newton was then engaged in 
writing. = 
But this was not all: Newton saw in the cosmic circulation 
and the mutual convertibility of rare and dense forms of matter 
a universal law, and rising to a still bolder conception, which 
* Brewster’s Memoirs of Newton, vol. i, pp. 121 and 404. 
