230 THE NORTHERN MICROSCOPIST. 
We had expected to find objects exhibited under the various 
microscopes manufactured by the leading makers during the past 
fifty years: the single lenses; the non-achromatic compound ; 
Pritchard’s jewel microscope; Wollaston’s doublets; Tulley’s 
achromatics ; The Amician reflector ; were all in limited use fifty 
years ago, and the same object displayed under each would have 
formed a starting point, from which the progress might have been 
judged. In 1830, Dr. Wollaston sent forth to the world his cele- 
brated doublet, consisting of two plano-convex lenses—fifty years 
have passed away, the doublet is a thing of the past, and therefore 
the student has only on special occasions the opportunity of seeing 
or even hearing of these antiquated instruments. 
In the Exhibition at Bootham’s Bar was to be found a case of 
instruments lent by the Science and Art Department, Kensington 
Museum, containing optical apparatus chiefly of foreign manu- 
facture, Fresnel’s rhombs; Iceland spar cut in three directions, 
perpendicularly, parallel, and obliquely to the axis; and a polariz- 
ing microscope, with lens for parallel light and prism for measuring 
the axes—all made by Laurent of Paris. Norremberg’s polarizing 
apparatus, made by Lutz of Paris, and a Refractometer on Prof. 
Abbe’s system, made by Carl Zeiss of Jena, were also shown. In 
this case also was to be seen Dr. Goring’s engiscope (compound 
achromatic microscope) which has been illustrated in Pritchard’s 
“Microscopic Illustrations,” and this was the only instrument in 
this exhibition giving the observer any idea of what a modern 
microscope was. 
_ Wending our way to the Assembly Rooms in Blake-street, where 
we were informed was a Loan Museum, we entered the corridor by 
a few exceedingly steep and inconvenient steps, to find ourselves 
in the midst of a number of workmen busy in all directions re- 
moving the tinsel, the remnants of the previous night’s soirée. No 
one seemed to know where the celebrated exhibition of scientific 
apparatus was being held, and the absence of any placards 
seemed to indicate that we were travelling in the wrong direction. 
We pursued our course nevertheless, and eventually found ourselves 
in the Concert Hall, where half-a-dozen people were wandering 
about evidently like ourselves on a voyage of discovery. 
Upon a table or bench on one side of the room stood a micro- 
scope owned by the Rev. W. H. Dallinger, made by Messrs. Powell 
and Lealand, with the microscope lamp used by this observer in 
his researches upon “the life history of a minute septic organism.” 
The object of this lamp is to secure minute and delicate adjust- 
ments in the position of the flame image upon the mirror or prism, 
since it has been found by the exhibitor that perfectly central 
illumination can only be secured by having the image of the flame 
exactly under the optical axis of the sub-stage combination, after 
