by compression in a mould, formed of a brass barrel, six inches and 

 a half long, and turned rather taper within, so as to facilitate the ex- 

 traction of the ingot when formed. The platinum is first subjected 

 to a partial compression by the hand with a wooden plug, so as to 

 expel the greater part of the water. It is then placed horizontally 

 in an iron press, of which a figure is given, constructed so as to afford 

 great mechanical advantage to the power applied to produce com- 

 pression. The cake of platina is then to be heated to redness by a 

 charcoal fire, in order to drive off all the remaining moisture ; after- 

 wards subjected to the most intense heat of a wind furnace ; and 

 lastly struck, with certain precautions, while hot, with a heavy ham- 

 mer, so as effectually to close the metal. The ingot thus obtained 

 may, like that of any other metal, be reduced by the processes of 

 heating and forging to any other form that may be required. It 

 may then be flattened into leaf, drawn into wire, or submitted to any 

 of the processes of which the most ductile metals are capable. 



The perfection of the above method of giving complete malleability 

 to platina, is proved by comparing the specific gravity of a fine wire 

 of that metal obtained by this process, which is found to be 21'5, 

 with that of a similar wire drawn from a button which had been 

 completely fused by the late Dr. Clarke with an oxy-hydrogen blow- 

 pipe, and which the author ascertained was only 21 '16. A further 

 proof of the excellence of the method employed by the author is de- 

 rived from the great tenacity of the platina thus obtained, as deter- 

 mined by a comparison of the weights required to break wires made 

 of this metal, so prepared, and similar wires of gold and of iron. 

 These weights he found to be in the proportion of the numbers 59, 

 50, and 60 respectively. 



An account is subjoined of the process employed by the author for 

 obtaining malleable palladium by the intermedium of sulphur ; and 

 also of that for procuring the oxide of osmium, in a pure, white, and 

 crystallized state. 



A Description of a Microscopic Doublet. By William Hyde Wol- 

 laston, M.D. F.R.S. S(C. Read November 27, 1828. [Phil. Trans. 

 1829, p. 9.] 



The author, considering that in all microscopes distinct vision is 

 impeded instead of being assisted by whatever light may be thrown 

 upon the object beyond what is fully commanded by the object-glass, 

 obviates this evil by collecting the admitted light to a focus in the 

 same plane as the object to be examined. For this purpose he em- 

 ploys a plane mirror to direct the light, and a plano-convex lens to 

 collect it, the plane side of the lens being towards the. object to be 

 illuminated. Availing himself of the property possessed by that form 

 of eye-piece for astronomical telescopes, called the Huygenian, of 

 correcting both chromatic and spherical aberration, the author con- 

 ceived that by applying to a microscope the same combination re- 

 versed, he might obtain similar advantages. The construction he 



VOL. II. 2 A 



