121 



had found, that the qualities of hardness, whiteness, and 

 indisposition to contract tarnish, necessary to a speculum, 

 could not, by any admixture that I could hit upon, be 

 produced, unless the metal were so highly satvuated with 

 tin, as to be excessively brittle; and because I found that 

 this brittleness, however inconvenient in some respects, was 

 necessary to render it susceptible of the highest polish : for 

 no metal yet known, except steel, (which, from its disposition 

 to rust, is unfit for this purpose,) will take as high a polish as 

 glass will, unless it be more brittle than glass. And indeed 

 this property is common to all substances which Ave know, 

 that are capable of such polish: they must be very hard, 

 and, as such, brittle; for the polishing poAvder employed 

 would stick and bed itself in any soft metal, instead oi 

 cutting and polishing it. * • 



From the result of my trials, I contented myself with the 

 composition mentioned hereafter, as being in every respect 

 sufficient for the purpose, and inferior to none in whiteness, 

 lustre, and exemption from tarnish: for, as to the addition 

 of silver, I found that, Avhen used even in a very small quan- 

 tity, it had an extraordinary property of rendering the metal 

 so soft, that I Avas deterred from employing it : and unless it 

 shall be found that, Avithout this effect, it makes the metal 

 less porous than otherwise it might be, or .less frail and brit- 

 tie, I am certain that jt may, in every fitjher respect,. ,^e dis- 

 pensed Avith. I had no opportunity to try it, in the precise 

 quantity Mr. IklAvards i-econmiends, (though! did so before, 

 in very' jne^rlj^^thatgprop9^ sjuce I first3|a\y,||ji|^' 'nigiRoii; 



