18uo.] Zoology and Botany. Ill 



periods of time, or for the same time, to light of different degrees of 

 intensity, their tints would be found to vary in the same ratio as the 

 light or the time. The time during which the papers were exposed 

 was read off by the pendulum photometer, and the degree of tint 

 attained was examined by the light of a soda flame. 



Professor Eogers then described various pieces of apparatus which 

 he had devised for testing illuminating gas chemically and photo- 

 metrically. In the photometric testing he had discarded the candle, 

 which was very inaccurate, and used a lamp in which was burnt oil of 

 a certain specific gravity. The description of the various pieces of 

 apparatus could not be rendered intelligible without diagrams. 



Dr. Paul, in a paper " On Useful Applications of Slag from Iron 

 Smelting," suggested the grinding it to dust, and mixing it with lime, 

 when it could be moulded into bricks by powerful pressure. These 

 bricks required no fire, but could be used at once, the influence of the 

 atmosphere producing a slow kind of hardening. 



Zoology and Botany. (Section D.) 



An interesting account of the recent successful attempt to introduce 

 the ova of the salmon into Australia, was read by Mr. T. Johnson. — 



In January, 1864, 181 boxes of common deal, measuring 12 inches 

 by 9 inches, by 5 inches deep, containing upwards of 100,000 salmon 

 ova and 3,000 trout ova, were arranged in an ice-house, holding over 

 30 tons of Wenham Lake ice, on board the ship ' Norfolk.' On 

 arriving at Melbourne, 11 boxes were retained, and the remainder for- 

 warded to Tasmania. The ova were deposited in properly prepared 

 gravel beds ; and of the 103,000 sent out, upwards of 31,000 were 

 alive. The death of so many on the voyage was ascribed partly to 

 some of the ova not being in the best condition at starting, partly to 

 the moss on which they were laid being in bad order, partly to some 

 of the ova being frozen before starting, and lastly, to the bilge-water 

 of the ship entering the ice-house. Considerable mortality also took 

 place amongst the ova after being deposited on the gravel beds, but 

 diminished as the season grew colder. The first fish was hatched in 

 Tasmania on the 4th, in Melbourne on the 7th of May ; the last 

 on the 8th of June, 54 days after arrival at Tasmania, and 147 days 

 after impregnation. On the 20th of June only 3,300 of the young 

 fish were alive and healthy, so great has been the mortality amongst 

 them. The author invited the co-operation of salmon-breeders, 

 in order to determine the cause of this mortality and devise means to 

 check it. 



Dr. Daubeny read a paper, in which he assumed as an acknow- 

 ledged fact, that species, as well as individuals, have a limited period 

 of existence, but that certain natural contrivances are provided for 

 postponing this inevitable termination to a later period than would 

 otherwise happen were not such a provision made. It was suggested, 

 that in the vegetable kingdom, the introduction of new varieties was 

 an important means of prolonging the life of a species. 



VOL. II. N 



