112 



PROCEEDINGS OF THE SOCIETY. 



MEETING 



Held on the 18th Decembee, 1912, at 20 Hanover Square, W., 

 Mr. p. E. Radley, Vice-President, in the Chair. 



The Minutes of the Meeting of the 20th November, 1912, were 

 read and confirmed, and signed by the Chairman. 



The List of Donations (exclusive of exchanges and reprints) re- 

 ceived since the last Meeting was read as follows, and the thanks of the 

 Society were voted to the donors : — 



From 

 C. E. Heath, The Beginner's Guide to the Microscope. (1912) The Publishers. 



Proceedings and Transactions of the Liverpool Biological Society,! The Liverpool 

 xxvi. (1912) / Biol. Soc. 



Mr. Barnard exhibited and described a small arc-lamp, made at his 

 suggestion by Messrs. Baker. Mr. Barnard said that small electric arc- 

 lamps are now used in various branches of microscopical work. They 

 are designed to take currents of from 4 to 5 amperes, and are used for 

 purposes such as dark-ground illumination or photomicrographic work, 

 where exceedingly short exposures are not essential. They have the 

 particular advantage that they approach more nearly than any other 

 to the ideal source of light, the source itself being very small in area and 

 of great intrinsic brilliance. The type that appears to have come into 

 general use is that in which the carbons are at right angles to one 

 another, the positive carbon being the horizontal one, the negative being 

 in a vertical position. The carbons are adjusted by means of a simple 

 hand-feed mechanism. Probably Messrs. Leitz were the first to in- 

 troduce a really practical lamp of this type, and their lamp is to-day a 

 very good example of a simple arrangement of this description. 



The one described this evening was made by Messrs. Charles Baker, 

 of High Holborn, at his suggestion. So far as its mechanical details 

 are concerned, there is nothing very characteristic except that the body 

 part is open, and therefore the mechanism is not likely to get hot. The 

 carbons are fed by means of screws, which are geared so that the rate of 

 feed is adjusted to compensate for the unequal size and rate of consump- 

 tion of the carbons. The positive carbon is cored, and is preferably the 

 thinner one. In this connexion he ventured to suggest the opinion that 

 as a rule in such lamps this is the best method to adopt. The luminous 

 crater on the positive carbon should, in a right-angle carbon lamp, 

 occupy as nearly as possible the whole of the end of the carbon. It is 

 one of the features of these lamps that to ensure success they must have 



