Jeremy Bentham

T. L. S. Sprigge (ed.), The Collected Works of Jeremy Bentham: The Correspondence of Jeremy Bentham, Vol. 1: 1752–76

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Editor’s Note152To Samuel Bentham24 February 1776 (Aet 28)

A Diner chez les 3 Tons.

J'ai été parler avec Poore ce matin: et j'en ai tirè; des avis très utiles. Je l'ai trouvè parfaitement instruit de tout ce qui regarde pg 299L'Horologerie. Pour te faire plaisir (pour ne pas dire davantage) en deux Mots—(mais ne va pas me chicaner sur le nombre)—Votre projet est nouveau: je l'en ai trouvè bien persuadé. Mais aussi vous fait il des objections bien instructifs et bien dignes de votre attention. Je ne sais pas si il y en a contre lesquelles vous n'êtes pas en garde. A Pendulum clock it cannot be. To keep such an one on board ship is found absolutely impracticable even with all contrivances of Gymbols etc. etc. It must be a Watch that is a Time piece that goes by a Spring—there are it seems no other primum mobilia in use. A watch must be wound up not seldomer than every 15 or 18 hours: how will you wind it up so often? It must not be taken out. that sudden change from hot to cold you know would derange the whole æconomy of the Spring. This I believe you are aware of. 2. There is no knowing a priori how metal may perform in a degree of heat so much superior to that of the atmosphere. This however is to be apprehended. The teeth and pinions etc. etc. which fitted on the heat of the atmosphere will fit now no longer. It is not certain that they will expand in proportion—the female parts of the work may no longer admitt the male : at least to play with equal freedom as before. Metals specifically the same are composed of strata of unequal densities and degrees of expansibility. The rate of expansibility between two strata may in different degrees of heat be different.

Courage mon ami. It was in obviating the inequalities of expansion that Harrison's2 time-pieces were principally deficient. He could temper by long practise a piece of metal I should say combination of metals so as to make it answer the purpose: but then he could not give any principles—any rules whereby apparatus's could be made. Your plan is unembarassed by these difficulties. You must now go to watch boiling. Take your old watch (I believe I have got it here) observe how it goes during a given time in the heat of the atmosphere. Then afterwards in one of your contrivances. I can now no more—Poore is perfectly communicative and perfectly ready as far as seemeth to assist you in everything in his power. He promised secresy : which I hope he will keep.

24 Feby. 1776.

1 expect your Shirts by Tuesday.

pg 300Let me hear from you soon—you received one I suppose from me 4 days or two ago.

I need scarce tell you that Poore commended the invention.

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Editor’s Note
152.1 B.M. II: 8. Autograph.
This letter concerns a project of Samuel's for solving the problem of accurate timekeeping and hence navigation on sea voyages (cf. letter 156). He hoped to gain one of the rewards offered by the Board of Longitude for improved methods of determining the longitude at sea. Jeremy consulted his friend Poore about it, as he had in the case of Samuel's chain pump scheme (see letter 96, n. 5), and himself prepared the Memorial on the scheme which was to be put before the Board of Longitude.
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