806 PROCEEDINGS OF THE SOCIETY. 



the purpose, but he could at any rate voice the sentiments of the Society 

 when he expressed his very great gratitude to Professor Thomson for 

 taking the trouble to bring up the beautiful specimens exhibited — in 

 itself a Herculean task — and for showing the lovely drawings, without 

 which those who understood but little of this particular branch of 

 biology would have had some difficulty in following. The question of 

 the paraffin bath he would prefer to leave severely alone, as he had not 

 the faintest idea for what it would be used. The aerator, however, 

 seemed to be a very wonderful apparatus, and for those who could not 

 aerate their own aquaria (as he thought the majority did by oxygenating 

 the water with green algae), it would be a god-send. He was bound, 

 however, to confess that he regarded with a somewhat jaundiced eye an 

 apparatus which could produce minor species in a finger bath. He might 

 have misunderstood the President when he said that the inventor of this 

 apparatus had added three new species to the particular fauna found on 

 the Clyde by means of this aerator, but he could not help recalling to 

 his mind the communication made by himself and Mr. Earland at the 

 last meeting of the Society, when he pointed out that three varieties of 

 a species of foram had been successfully born in their aquarium, in con- 

 sequence, as they thought, of the starved condition in which they 

 were kept. He therefore looked to Professor Thomson to make clear 

 to them whether the new species mentioned by Dr. Gemmill were really 

 new species or varieties, or whether they were unfortunate abortions 

 as the result of living in the company of an apparatus of the character 

 described. 



The President said that for the sake of Dr. Gemmill's reputation he 

 would hasten to say (if he might do Mr. Heron Allen the injustice of 

 taking him seriously) that what Dr. Gemmill did was to establish from 

 among the animals in his aerated tanks three new records for the Clyde. 



The vote of thanks to the President proposed by Mr. Heron- Allen 

 was carried unanimously, and a hearty vote of thanks accorded to 

 Dr. Gemmill for his communications. 



A paper was read by Mr. Barnard, " On the Use of a Metallic Electric 

 Arc in Photomicrography." 



Mr. Rheinberg said that he would like to ask Mr. Barnard in con- 

 nexion with this interesting method whether he could state approxi- 

 mately the relative luminosity of the cadmium-silver arc as compared 

 with the ordinary carbon arc light using the same amount of current. 



Mr. Barnard replied that in the case of the cadmium-silver arc the 

 light-energy is concentrated in certain bright lines, and in the region of 

 these lines the luminosity was much greater than in a carbon arc. 



Mr. Rheinberg said he was speaking from the point of view of length 

 of exposure. 



Mr. Barnard replied that the exposure would be less with the 

 cadmium-silver arc, assuming that exactly the same regions of the 

 spectrum were used for comparison. 



Mr. Maurice Blood asked if it would be possible to use a carbon arc 

 with a metallic core ? 



Mr. Barnard replied : No. With a metal like cadmium the whole of 



