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 he 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 11 a demi-mot” and “ sctno 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 (Geneva and Paris). 
This treatise is divided into four books. 
I. “ Exposition sommaire clu 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. 
