1899] MICROSCOPICAL JOURNAL. 205 



stand has to support and focus, without tremor or oscil- 

 lation, a considerable weight of apparatus. My own sub- 

 stage, for example, fitted with an achromatic condenser, 

 which by the way, is always in position, weighs not less 

 than 1 ft). 6 oz. Unless, therefore, the mechanism which 

 sustains and moves this load be substantially and accu- 

 rately constructed, it is obvious that the strain will inevi- 

 tably disarrange the necessarily delicate adjustments of 

 the instrument. 



In my opinion, which has not been formed without con- 

 sultation with experienced workers in this metal, it is 

 in the construction of the substage and the apparatus 

 supported thereby, as w6ll as in that of the double or 

 triple nosepiece, that aluminium, as a much lighter substi- 

 tute for brass, seems to promise to be useful. That sub- 

 stages, and indeed complete microscopes of great perfec- 

 tion, can be made of this metal, or rather of one of its 

 alloys, has been abundantly shown by Messrs. Swift at 

 one of our recenfmeetings ; and although opinions may 

 differ as to the advisability of constructingany but a por- 

 table stand, like the one shown bv Mr. Swift, exclusively 

 of aluminium, it will, I think, hardly be contended that 

 anything but advantage could result from the use of this 

 metal in the manufacture of the substage and the appa- 

 ratus which it supports. 



Turning now to the optical portion of the microscope, 

 there is no doubt that within the last few years most im- 

 portant advances have been made towards perfection. 

 Even during the last twelve months, or at any rate with- 

 in the last two years, more than one optician has added a 

 contribution to the resources of the microscopist. By 

 the use of several different varieties of Jena glass, opti- 

 cians are daily vieing with one another in the perfecting 

 of apochromatic objectives without the use of fluorite in 

 their construction. Only recently a new glass of 1-lOth 

 inch focal length and of 1.30 N.A. has been constructed 



