570 Meeting of the British Association. [Oct., 



solution of gelatin, containing a little sugar and chromate of potash, 

 over a glass plate previously coated with collodion. The film sets 

 on cooling, and is then placed in contact with an ordinary photo- 

 graphic negative of the microscopic objects to be delineated, exposed 

 to light, submitted as before to the action of water, and the soluble 

 portions washed away. When the surface-moisture has evaporated, 

 a mixture of plaster of Paris, containing a small proportion of alum, 

 is poured over the relief to the thickness of half-an-inch, and left to 

 set. When dry it will be found, owing to the alum in the plaster 

 having hardened the surface of the gelatin directly on coming in con- 

 tact therewith, to leave the gelatin easily, without any fear of adhe- 

 sion. To give a finished appearance to the resulting casts, this 

 intaglio, when dry, may be placed in a lathe, and a suitable border 

 turned on it, which will be represented in the resulting proofs by a 

 raised border, similar to what is seen on medallions or plaster casts. 

 The name of the object may also be neatly engraved on the intaglio, 

 to appear in raised characters on the reliefs. This intaglio should 

 then be well waxed to fill up the pores, and is ready for taking any 

 number of impressions in plaster ; or a better plan is to take one in 

 plaster, and having smoothed away any defects to mould a reverse 

 in sulphur, which will give a greater number of fine impressions. 



The author finally alluded to the subject of photolithography, 

 as used in the photographic establishment of the War Department, 

 at Woolwich. m 



Mr. Crookes then described his " New Polarizing Photometer." 



Geology. (Section C.) 



Although a large number of valuable papers were communicated 

 to the Geological Section of the British Association at Dundee, 

 there were few which, from their originality or largeness of con- 

 ception, were calculated to leave a lasting impression on the minds 

 of those present. There was no announcement of a new system of 

 rocks — of a new theory of metamorphism — or of the annihilation 

 of some generally received and cherished doctrine. The papers 

 were on the whole fragmentary treatises on matters of detail — 

 bricks and stones intended to occupy their special nitches in the 

 temple of Science — and as such not without their value. Nor can 

 we shut our eyes to the fact, that such must be the general 

 character of the investigations of future geologists. Far be it from 

 us to assert that this branch of Science is incapable of presenting 

 new facts, and of giving rise to new speculations, regarding the past 

 history of the globe and its inhabitants ; but we are now sufficiently 

 well acquainted with the order of succession of the groups and 



