Description of a Hydrometer. 329 
every engineer in this mechanical country; the only real credit 
that can be acquired in this pursuit, will be given to those who 
do actually realize the invention, and this will be due to each in- 
dividual in proportion to the liberality with which he supports 
the undertaking. 
Large individual subscriptions however are not necessary to 
obtain 15002. and in fact subscriptions of one guinea are often 
more productive than those of a hundred. But whatever gentle- 
men may think proper to subscribe, whilst the subject is before 
them, I would request them to give notice of immediately, as by 
that means, and that alone, can any further step be taken be- 
fore the subject will be forgotten. 
I remain, sir, 
Your obedient servant, 
Brompton, April 5, 1816. Gro. Cayley. 
P. S.—The sketch represents an end view of a hydrogen gas 
balloon with three tiers of wing to be worked by the steam- 
engine, or any other first mover; each wing to be divided into 
many stripes or portions, which are so constructed as to heel up 
and down by the alternate pressure of the air above and below 
them at each stroke of the engine, and thus by their oblique 
waft to propel the balloon. 
LXV. Description of Mr. Pxititips Lonpon’s Hydrometer; with 
Remarks on the curing of Mackerel for Exportation or Win- 
ter Use*. 
Sir, — I HEREWITH send you a half barrel of mackerel, part 
of twenty-five thousand mackerel cured on my plan; also Mr. 
Cutler’s certificate, that so many were cured at Ramsgate du- 
ring the last season, most of which were shipped for Russia. 
They were all cured by immersion in brine of British solid salt, 
agreeably to the method I had the honour of communicating to 
the Society, and which is printed in the thirty-second volume of 
the Society’s Transactions, p.204. The whole were extremely 
fine, and full as beautiful as the specimen sent, which | hope will 
“meet the approbation of the Society, 
I am, sir, 
Your obedient servant, 
No. 57, Cannon-street, London, Puiiiies Lonpon. 
Feb. 14, 1815. 
To.C. Taylor, M.D. Sec. 
* From Transactions of the Society for the Encouragement of Arts, Manu- 
Suetures and Commerce, vol. xxxili. for 1815.—The Society’s silver medal 
set mm gold was voted to Mr, London fur this coinmunication. 
‘ From 
