PROCEEDINGS OF THE SOCIETY. 531 



possible, and then having used the whole aperture, the light should 

 afterwards be reduced to sharpen the object. To insure success, ex- 

 tremely accurate focusing was necessary, and to obtain this it was well 

 to put a plate on with some object mounted upon it — say, some diatoms. 

 This was easily obtained by pouring a little water containing diatoms 

 upon the glass and letting it evaporate, when the diatoms would be left 

 adhering to the glass ; then focus and get an aerial image. He quite agreed 

 as to the value of the quarter- plate size. It was undoubtedly the most 

 useful for lantern plates and for enlargements, and he entirely concurred 

 as to the benefit to be obtained from taking negatives first on a smaller 

 scale and enlarging afterwards ; but he had very decided opinions as to 

 the uselessness of diaphragms behind the object. 



Dr. Kibbler said as regarded the hairs he could only say that the 

 image of the object when seen on the ground glass appeared very much 

 worse than in the photograph, each hair showing as if composed of three 

 or four. The photograph was not taken with a small diaphragm. It 

 had an exposure of ten minutes with an ordinary paraffin lamp. If he had 

 a good light he could demonstrate to any one in the room the use of the 

 diaphragm plate in improving the image when used in the way he had 

 described. With small objects like blood-discs diffraction images 

 appeared. 



Mr. Crisp said that since their last meeting various London and 

 provincial papers had published a most astounding piece of rubbish in 

 reference to an alleged " new glass just made in Sweden." Many of the 

 Fellows and others had forwarded cuttings to the Society {supra, p. 499). 



Mr. Crisp also called attention to the fact that the 14th (1888) 

 edition of Heather's ' Mathematical Instruments ' had been issued, with 

 the descrij)tion of the Microscope which was given in the first edition 

 unaltered and uncorrected. In particular, it is made to appear that the 

 " amplifying lens " of bygone days is, with the eye-lens, field-lens, and 

 objective, an essential part of a compound Microscope, while a whole 

 page is devoted to the reflecting Microscope, none of which have been 

 made since 1840 {supra, p. 501). 



Mr. Mills's note on " A Sponge with Stelliform Spicules " was read 

 by Prof. Bell. 



Mr. Crisp referred to some comments which had recently been made 

 in America upon the advantages of the method of tilting the stage of the 

 Microscope as a means of obtaining a very economical and simple fine- 

 adjustment. This idea was not by any means new, as might be seen by 

 an examination of the various Microscopes upon the table, in each of 

 which it had been carried out in a different way {supra, p. 478). 



Mr. J. Mayall, jun., said his main objection to this form of fine- 

 adjustment was that for high powers it was not possible to properly use 

 a condenser. Focusiug by tilting the stage not only involved the move- 

 ment of the object in relation to the objective, but also in relation to the 

 substage condenser. Under such circumstances he thought it was hardly 

 possible to carry on a delicate microscopical investigation satisfactorily. 



Mr. Beck said that to allow the stage to move in any direction except 

 parallel to its plane, at once destroyed all delicate effects. Let them 

 take such an object as a Podura scale, and they would find that if they 



