168 J. MATTHEWS ON THE MICRO-MEGASCOPE. 



body of the microscope. It was also erected and varied in size and 

 definition with the power used, as also with the distance of the object. 



But I soon observed not only that it was difficult to illuminate a 

 translucent object placed below the stage, but that the distance to 

 which that object could be removed, was practically limited by the 

 height of the microscope above the table ; unless, indeed, the in- 

 strument were placed horizontally, which was not a convenient 

 position in practice. To remedy this, I thought of adjusting a 

 translucent object or slide to the flat side of an ordinary condenser, 

 in the usual place between the lamp and the microscope, so that its 

 image might be reflected by the plane mirror upwards through the 

 substage objective. This plan effected exactly what was required 

 by diverting the line of sight in such a manner that it was possible to 

 place the object at any distance, and its image being thus varied in 

 size, might (or could) be exactly included in the usual field of the 

 microscope, and when there, easily examined by objectives and eye- 

 pieces of almost any power. By this simple plan the powers and uses 

 of the instrument were immediately increased, practically without 

 limit, as I will now proceed to show. The objectives of the lowest 

 powers which have hitherto been used are the 5 and the 4 inch. Now, 

 with the ordinary A eye-pieces, the diameters of their field of view are 

 ( about) '5 and '4 of an inch only, and so on with th e other lowpowers 

 — the field, of course, lessening in degree. But there are many objects, 

 such as large sections of woods, insects, corals, and various other things, 

 which it is often most desirable to see wholly, and then to examine 

 in detail. This is obviously impossible by any means hitherto used, 

 except the lantern and the erector. Of the former I need not speak. 

 The uses of the latter are so limited, that it has met with very little 

 favour of late years, although it is very useful where the object 

 " requires any kind of manipulation," or " where an extensive and 

 yet limited range of magnifying power is required without any 

 change in the objective." — (Carpenter.) 



By this new arrangement, the object suitably illuminated is placed 

 just so far from the mirror as to fill, when examined by the usual 

 objective, preferably a two-inch and A or No. 1 eye-piece, the whole 

 of the field exactly. There is no doubt that, in principle, the micro- 

 scope is thus converted into a telescope of any power that may be 

 required. 



The ordinary achromatic condenser has always been focussed by 

 examining the image of the flame of the lamp, or that of the bars 



