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XXVI. — On a White Mirror for the Microscope. 

 By George C. Handford, Esq. 



(Read December II, 1850). 



As the subject of illumination is of so much importance to micro- 

 scopical observers, I feel that there is scarcely any necessity for apo- 

 logy from me for intruding upon the time of this meeting, in making 

 a few remarks on some of the defects in the means of illumination 

 now in use, and in bringing to your notice a white mirror, which I 

 have made with a view to remedy them. 



In viewing objects by lamp-light, which are illuminated by the sil- 

 vered mirror, there is generally a great glare of reddish-yellow light, 

 which is very injurious to the sight, and the object is in many cases 

 almost obliterated. If it is attempted to lower the flame of the lamp, 

 or to throw off some of the rays by moving the mirror, the definition 

 of the object is interfered with ; and the same effect takes place on 

 cutting off the light, by means of the diaphragm, or by altering the 

 quantity of light in any other way. 



With the white mirror these defects are, I may say, entirely reme- 

 died ; and if with a low-power object-glass there should be a little 

 too much light, the flame of the lamp can be lowered, or the mirror 

 altered, without producing the objectionable result before mentioned, 

 and the diaphragm is not needed. 



These facts cause me to suppose, that the quality of the light 

 transmitted to the object-glass by means of my mirror is much more 

 pure than by that now in use. 



The white mirror consists of a thin, concave glass, three inches in 

 diameter, the back of which is rendered white by means of plaster of 

 Paris, or zinc paint ; and it is mounted in brass, and fits over the 

 frame of the silvered mirror, without requiring the latter to be in 

 any way altered. 



Mirrors to answer the same purpose could be made of white mar- 

 ble ground concave and polished, or of white opaque glass rendered 



