%78 M. Gay Lussac's Reflections on Volcanoes. 
<c Up in-land rivers, where the bottom can possible be reached, 
the fans may be taken out, and cranks placed at the hindmost 
axis to strike a shaft to the bottom of the river, which will drive 
the vessel forward with the greater force. 
<c Query III. — It being a continual expence to keep this ma- 
chine at work , will the expence be answered ? 
“ Answer . — The work to be done by this machine will be up- 
on particular occasions, when all other means yet found out are 
wholly insufficient. How often does a merchant wish that his 
ship were on the ocean, when, if he were there, the wind would 
serve tolerably well to carry him on his intended voyage, but 
does not serve, at the same time, to carry him out of the river, 
&c. he happens to be in, which a few hours 1 work of this ma- 
chine would do. Besides, I know engines that are driven by the 
same power as this is, where materials for the purpose are dear- 
er than in any navigable river in England ; therefore, experi- 
ence demonstrates, that the expence will be but a trifle to the 
value of the work performed by those sort of machines, which 
any person that knows the nature of those things may easily cal- 
culate. 
“ Thus, I have endeavoured to give a clear and satisfactory ac- 
count of my new invented machine, for carrying vessels out of 
and into any port, harbour or river, against wind and tide, or in 
a calm ; and I doubt not, but whoever shall give himself the 
trouble to peruse this essay, will be so candid as to excuse or 
overlook any imperfections in the diction or manner of writing, 
considering the hand it comes from ; if what I have imagined, 
may only appear as plain to others as it has done to me, viz. 
that the scheme I now offer is practicable, and, if encouraged, 
will be useful. J. H. 11 
Art. XV. — Reflections on Volcanoes . By M. Gay Lussac. 
Before indulging in some reflections upon volcanoes, a 
wide field which has been long open to conjecture and hypo- 
thesis, I must commence with declaring that I am not in pos- 
session of the knowledge requisite for treating of such a sub- 
ject in full, and that I shall only glance at it, confining myself 
