17 



Mr. Wm. Kirkbj exhibited a large collection of seeds. 



The chairman briefly described a series of lantern slides of typical 

 examples and structures of insects which were thrown on to the screen. 

 Specimens were also shown under the microscope. 



Meeting held in the Club's Eooms, 80, Municipal Buildings, April 

 8th, 1889. J. Lewkowitsch, Ph.D., F.O.S., in the chair. 



THE INTERrKRENCfi OF LIGHT IN RELATION TO THE COLOUR OF FEATHERS 



AND OTHER OBJECTS. 



F. W. BRANSON, F.I.C., F.C.S. 



The undulatory theory of light was first discussed, and shown to be 

 capable of satisfactorily explaining the phenomenon of interference of 

 light, as a result of which objects devoid of colour appear variously 

 coloured according to the angle of the illuminating ray. Interference of 

 light was shown to result when the paths of two nearly parallel pencils 

 of light intersect. The coloured spectrum of white light was shown ou 

 the screen, and white light was shown to result from the blending of 

 the coloured prismatic tints which are visible when white light i.s passed 

 through a prism. Two methods whereby colour is produced by means 

 of interference of light were then discussed, viz., reflection from a very 

 thin film, e.g., a soap bubble, or an oily layer ou water, and reflection 

 from a minutely-grooved or closely striated surface, as in many 

 feathers. 



A number of objects interesting to the naturalist were then shown 

 and explained — objects which owe their colour wholly or partially to 

 interference, viz., feathers of peacock and humming bird, elytron of 

 beetle, wing of moth, &c. 



J)r. Lewkowitsch supplemented the paper with some observations. 



Meeting held in the Club's Eooms, So, Municipal Buildings, April 1.5th, 

 1889, F. W. Branson, F.I.C., F.C.S., in the chair. 



PHOTO-MICROGRAPHr. 

 U. POCKLINGTON, F.R.M.S. 



In the introduction was given a short sketch of the history and present 

 state of knowledge in this pai'ticular section of photography, in which even 

 now, although some very excellent results have been achieved, there is 

 much to be done before it can be really useful in all kinds of micro- 

 scopical work. It was observed that micro-photography as compared 

 with hand drawing had the advantage of defining with the greatest 

 possible accuracy minute details of structure, and in a fraction of the time 

 that would be taken in ordinary drawing, but that is only as regards one 

 plane, and when objects are not of uniform thickness they turn out blurred. 



