582 Proceedings of the Royal Society 
therefore, are inevitable consequences of the supposed consti- 
tutions. 
2 d, Although I here present these constitutions crudely and 
without proof, as if they were gratuitous hypotheses and hazarded 
fictions, equitable readers will understand that on my own part I 
have at least some presumptions in their favour (independent of 
their perfect agreement with so many phenomena), but that the 
development of my reasons would be too long to find a place in the 
present statement, which may be regarded as a publication of 
theorems without their demonstrations. 
3d, There are details upon which I have wished to enter 
on account of the novelty of the doctrine, and which will readily 
be supplied by those who study it in a favourable and attentive 
spirit. If the authors who write on hydro-dynamics, aerostatics, 
or optics, had to deal with captious readers, doubting the very exist- 
ence of water, or air, or light, and therefore not adapting them- 
selves to any tacit supposition regarding equivalencies or com- 
pensations not expressly mentioned in their treatises, they would 
be obliged to load their definitions with a vast number of specifi- 
cations which instructed or indulgent readers do not require of 
them. One understands u cl demi-mot” and u sano sensu” only 
familiar propositions towards which one is already favourably 
inclined. 
Some of the details referred to in this concluding sentence of 
the appendix to his “Lucrece Newtonien,” Le Sage discusses fully 
in his “ Traite de Physique Mecanique,” edited by' Pierre Prevost, 
and published in 1818 (G-eneva and Paris). 
This treatise is divided into four books. 
I. u Exposition sommaire du systeme des corpuscules ultra- 
mondains.” 
II. “ Discussion des objections qui peuvent s’elever contre le 
“ systeme des corpuscules ultramondains.” 
III. “ Des fluides elastiques ou expansifs.” 
IY. “ Application des theories precedentes a certaines affinites.” 
It is in the first two books that gravity is explained by the im- 
pulse of -ultramundane corpuscules, and I have no remarks at pre- 
sent to make on the third and fourth books. 
