■"392 PROCEEDINGS OF THE 



'tub -shaped, while those of the Canary-shouldered Thorn had been 

 'Compared by some of the men at the Y.M.C.A. huts to petrol- 

 tins, which they very much resemble in shape — both these eggs 

 are brilliantly iridescent. The speaker thought that the egg of 

 the Waved Umber was one of the, most beautiful : its surface is 

 honeycombed, and at the corner of each hexagon there is an 

 iridescent pearly boss. The next photograph was of the egg of 

 a fly, Anthomia. These eggs, which are ivory-white, are covered 

 with a fine network of hexagonal markings, and Mr. OfEord said 

 that under a high power secondary dottings could be seen similar 

 to those occurring in some of the Diatomaceae — e.g., Triceratium 

 favus. The remaining slides were of the curious eggs of bird- 

 parasites. The parasite of the Hornbill lays an egg of an ivory 

 colour with a little cap at one end of it ; this egg difiers in form 

 according to the position on the feather in which it is laid. The 

 last three slides showed eggs that resembled flowers, that of the 

 parasite of the Japanese turkey being singularly like a chrysan- 

 themum. The chairman proposed a hearty vote of thanks to 

 the speaker, and asked him what form of illumination was used 

 in taking the photographs. Mr. Ofiord replied that he found a 

 lieberkuhn the best, as it gave a strong light, although better 

 relief was given by using the silvered side-reflector ; he used an 

 inverted gas-mantle with the air-pressure carefully adjusted as 

 the source of light. Mr. Bryce said that he was surprised 

 Mr. Offord had kept the photographs so long before showing them 

 to the Club, and Mr. N. E. Brown drew attention to the use of the 

 concave substage-mirror to focus the light on opaque objects, a 

 method of illumination which gave very satisfactory results. 



Mr. J. Grundy, F.R.M.S., then continued the address on 

 polarised light which he had started at the previous meeting. 

 He explained how it was that the best results in polarisation were 

 obtained by arranging the object-crystal with its axes at an angle 

 •of 45° to those of the crossed Nicols. He then dealt with circular 

 polarisation, and exhibited a portable table-polariscope, and ex- 

 plained how he used it. He also described various simple experi- 

 ments with the microscope, and demonstrated the passage of 

 •a ray of light through one and through two crystals of cakite. 

 Mr. Grundy explained that frequently the light reflected from the 

 sky and from all sorts of objects was polarised, and he exhibited 

 two pieces of apparatus which he used to detect this condition, 



