Astronomical and Nautical Collections. 359 



fall of the bung below a line touching the staves at the head. The 

 rule itself gives a perfectly correct result in casks that differ but 

 little from a cylinder ; and it maybe observed in the Hid and IVth 

 examples, that a great wake appears to require some little addi- 

 tion to be made to the content, and a small wake some subtraction : 

 and the casks 8 and 9, compared with 10, will also serve to indi- 

 cate the propriety of a similar correction. I shall explain, in a 

 separate note, the principles on which such a computation may be 

 made, if required ; but I am not confident, from the result of all the 

 cases I have examined, that the advantage of these minute correc- 

 tions would not be perfectly inconsiderable, in comparison with the 

 unavoidable irregularities of the forms of the casks, and the pro- 

 bable errors in their admeasurement ; especially as in any large 

 number of casks that are to be gauged at the same time, the errors 

 of the different casks being most commonly divided between the 

 opposite sides of the truth, would have a general tendency to neu- 

 tralise each other. 



On the whole, therefore, I have reason, to believe that the new 

 sliding rule alone will be found quite as accurate as can be required 

 for the ordinary purposes of the revenue, and that the simplicity of 

 its operation will be found to save much time and labour, and to 

 avoid all chance of error in computation ; and I trust that the 

 Board of Customs will be pleased to order some of its officers to 

 make trial of it in their practice on a large scale. 

 I have the honour to be, 

 Sir, 



Your obedient humble servant, 

 P. Delavaud, Esq., Thomas Young. 



&c. &c. &c. 



Note on the new Sliding Rule.- 



203 

 The formula represented by the sliding rule is this, Log. 



B + -21- Log. H + Log. L - Log. I 294 WG ) as Log. Content: 

 150 & ° B I 353 l.G / 



or otherwise B^saa x H 6 *6 7 x L : 294 = Content. The 



