Dr. Pearson's Observations 
43 8 
The composition in common use, which contains the greatest 
proportion of tin, is called speculum metal. The requisites of 
this metal are compactness, uniformity of texture, whiteness, 
sufficient strength to prevent its cracking in cooling, and to 
bear polishing without breaking. Mr. Mudge found the whole 
of these properties attainable in the greatest degree, by a little 
less than one part of tin with two parts of copper. But 
for very large instruments ; such as the 40-feet telescope of 
Dr. Herschel ; the proportion of tin must be less than in 
small instruments, on account of the property of brittleness. 
The compound of equal weights of copper and tin is so 
brittle, that it is not easy to conceive to what useful purpose it 
can be applied. 
The allays of tin with copper, by -which I mean those com- 
pounds of copper and tin in which the tin is in greater quan- 
tity than the copper, I believe, have not been examined. It is 
said, indeed, that tin allayed with a very small proportion of 
copper has been employed for tinning, to save much of the ex- 
pence of tin ; for a much thinner coat of this compound can 
be spread than of tin. 
viii. The next conclusion is founded on the experiments of 
the allays of copper with steel. 
It appears that copper may be united to steel without the 
interinede of any other metal ; for a perfectly homogeneous 
compound was produced by melting ten parts of copper with 
one of steel, § 6 . Exper. 19. As this allay was not harder 
than that of" copper with one-twentieth of its weight of tin, 
and as it did not appear that a compact and uniform malleable 
metal could be composed of one part of steel with two partsof 
copper, § 6 . Exper. 20. I thought it unnecessary to make any 
