474 



light could be projected by means of a mirror down one of the 

 tubes of a binocular microscope. For large objects a laryngo- 

 scope mirror was very effective for obtaining illumination at 

 a normal incidence. 



Objects suitable for examination are numerous, or perhaps 

 innumerable. Of thin plates — mica films, minerals that show 

 cleavage, feathers of humming-birds, scales of fish, beetles and 

 butter6ies are examples. Structures showing fine lines — artificial, 

 as in diffraction plates — or edge views and folds of thin plates, as 

 in mother-of-pearl. Mixed cases, as shown by white flowers in 

 sunshine, opal, felspar, etc., etc. 



Instances of the utility of the study of iridescence were noticed. 

 In the case of humming-birds it was desirable to be able to 

 describe their colours according to some uniform method. This 

 could be done by recording the colour shown by light reflected at 

 normal incidence, when the colour is found to be unvarying, dis- 

 appearing when the object is moved, but absolutely unchanged in 

 tmt. Such colours could be described as iridescent red, orange, 

 green, etc. Accuracy in colour nomenclature, and establishment 

 of standards of colour-comparison, would be assisted by these 

 methods of examination, and help would also be rendered in the 

 investigation of complex structures, for which ordinary micro- 

 scopic observation is inadequate. 



The President invited observations on Mr. Ingpen's very 

 interesting communication. He thought the Club owed their 

 thanks to Mr. Ingpen for bringing the subject before them. 

 Objects under the microscope lost nearly all colour. The diatom 

 Pleurosigma formosum flashes colours in sunlight, but under the 

 microscope it appears white. The resolution of structure is always 

 accompanied by loss of colour. It was really most beautiful and 

 interesting to look at iridescent colours given by ordinary bodies 

 viewed in suitable light. He had seen a number of jelly fish at 

 the end of a pier in deep water, against a dark background, and the 

 bright sun shining on their cilia gave a most magnificent play of 

 colours. He also referred to the beautiful colours on a soap 

 bubble, which were produced by the thinness of the film. The 

 wing of the dragon-fly also gave a beautiful tint for the same 

 reason. The most gorgeous colours, as Mr. Ingpen had said, were 

 found on the humming-birds. There was a fine collection at the 

 British Museum, which might be studied with advantage. One 



