October ^th, [gio^\ I'ROCEEDINGS. iii 



van lici Bataviaasch Gcnoo/Si/ia/^" pis. 1-12, door J. W. Teillers 

 (fol., VVeltevreden, 1910), presented by the Bataviaasch Genoot- 

 schap van Kunsten en \\'etens(happen ; " Scrmones Domini- 

 cales'\..elldtta Szilddy Aron, Kot. i, 2 (8vo., Budapest, 1910), 

 presented by the Magyar 'rudomanyok Akadeniia ; " The Trade 

 Winds of the Atlantic Ocean," by M. W. C. Hepworth, J. S. 

 Dines and E. Gold (4to., London, 1910), presented by the 

 Meteorological Office, London ; and " Geologic Atlas of the 

 f/i.S'.," folios 16-56, 5869, 71-168 (la. fol, Washington, 1895- 

 1909), presented by the U.S. Geological Survey. 



Mr. Thomas Thorp described a method for preventing the 

 tarnishing of silver-on-glass parabolic mirrors, which he had 

 found very successful. The method was, briefly, as follows : — • 



The mirror was carefully levelled on a turntable, and its 

 axis of rotation made coincident with that of the turntable. 

 The whole was then rotated uniformly at the calculated 

 speed required to cause a liquid to assume the same parabolic 

 form as that of the mirror. A i % solution of " Schering's " 

 celloidine in amyl acetate (after a lengthy period of settling) 

 was flooded on to the surface of the mirror to a depth of about 

 one-third of a millimetre. This was allowed to dry very slowly 

 when the resultant film was found to have a perfectly even 

 surface of a thickness of about ^-^ of a millimetre. 



On testing the mirror no perceptible loss of definition was 

 observed, and in actual use the performance was satisfactory. 



It is absolutely essential for the success of the method 

 that the mirror be quite enclosed, and exposed only to an 

 atmosphere of amyl acetate, so as not to be allowed to dry, for 

 about one hour after the solution has been flooded on, as, 

 without this precaution, a perfectly uniform film cannot be 

 obtained. 



Mr.C. E. SxROMiiYER, M. Inst. C.E., showed aprocess.nowfairly 

 well known to metallurgists, by which the sulphide segregations 

 in steel are reproduced on photographic paper which has been 

 steeped in a weak solution of sulphuric acid and then placed on 



