WA TSOWS NEW MICROSCOPE. 2Q 



is so pivoted to the substage arm as to allow the latter to 

 be swung aside and the mirror used alone when requisite, 

 without the trouble of taking the substage away altogether. 

 This is a great advantage, as it permits the substage, and 

 any apparatus it may be carrying, to be swung into or out 

 of position in a moment with the mirror in the position here 

 indicated. The stand has all the uses of the old forms of 

 microscope, and can be employed in exactly the same way, 

 but even then its peculiar motions round the object as 

 a centre give it very great advantages in every class of 

 investigation. But it is when the mirror occupies the 

 position now to be described that the peculiar properties 

 of the new stand are brought fully into play. 



The upright pillar, carrying the body and stage, is 

 attached at its foot to a massive circular plate, carrying a 

 graduated circle which rotates round a point exactly 

 beneath the centre of the stage ; and moving independently 

 and concentrically with this is another smaller circle, 

 having a dovetailed groove ploughed across it, into which 

 the mirror bar can be slid when withdrawn from the sub- 

 stage arm. A spring catch attached to the dovetailed 

 circle falls into a notch in the mirror bar when the centre 

 of the mirror is exactly beneath the centre of the stage. 

 This is the most useful position for the mirror, as a ray fall- 

 ing from a source of light upon it may be reflected upwards 

 perpendicularly upon the object, when the body of the 

 microscope is vertical, then without interfering again either 

 with the mirror or lamp, or interposing any accessory 

 apparatus whatever, but simply by inclining the body, the 

 light falls upon the object with a gradually increasing 

 obliquity until, when the instrument is nearly horizontal, a 

 perfect dark-ground illumination can be obtained even 

 with the highest powers, while the gradual way in which 

 the light becomes more and more oblique immediately 



