Notes. 



287 



1862, is in its original condition. The mounting of the body upon a 

 carriage which traverses an upright triangular post is evidently derived 

 from the Ross model of 1839. The flat tiipod foot, single pillar, and 

 compass joint, were a survival from preceding non-achromatic Micro- 

 scopes. It is important to note that this instrument has an achro- 

 matic condenser, and is therefore a very early example of one so fitted ; 

 because the achromatic condenser was, as we learn from the Penny 

 Cyclopaedia, introduced into this country from F ranee in 1839. Tlie 

 stage, which has Turrell's me- 

 chanical movements, is raised Fig. 78. 

 by means of a 50-thread fcrew 

 pushing under it three inclined 

 planes, placed at the periphery 

 of a rotating plate (slope 1 in 

 (i) ; the speed is therefore 

 ] /300 in. for each revolution. 

 All the motions throughout 

 the entire Microscope are tho- 

 roughly sprung. 



At this time Powell took 

 into partnership his brother- 

 in-law, Mr. P. H. Lealand ; 

 and under their joint names a 

 Microscope (fig. 78), upon an 

 entirely different plan, was 

 brought out; it is figured in 

 the frontispiece of Cooper's 

 Microscopic Journal for 1841, 

 and described at page 177, 

 but the working parts are 

 better shown in the plate in 

 the Transactions of the Society 

 of Arts.* In the general de- 

 sign of this Microscope, both 

 as regards the mounting of 

 the body on the grooved limb 

 and the double pillar support, the influence of Mr. George Jackson 

 will be at once recognised, and this' is the first instrument, so far 

 as is known, in which these two ideas of his were carried out. It 

 should be remembered in this connection that Jackson introduced 

 three things in Microscope construction : first, the grooving of the 

 Lister limb ; secondly, the double pillar | ; and thirdly, the ploughing 

 of the body and substage slides in one cut. It is interesting to note 



* Vol. liii. p. 78 (April 1841). 



t According to Quekett, the double pillar was introduced by George". Jackson in 

 1S38, but I have been unable to find any example or notice of it prior to this Micro- 

 scope of Powell's in 1841. 



