The Lantern Microscope. By Lewis Wright. 201 



results. I have not however, up to the date of this, yet found a 

 1/4 or 1/5 which gives a flat image, and shall feel exceedingly- 

 obliged for the loan, or trial under the owner's eye, or from any 

 maker, of any promising objective. The most suitable angle is 90° 

 to 100°. 



The objectives screw into a short jacket or body, which has a 

 sHding fitting into a socket. Thus by providing an extra jacket, 

 powers can be rapidly changed. 



A very important accessory to the objectives is a concave 

 amplifier. Though it would be necessary to have one calculated 

 for each objective to obtain perfect results with this, sufficiently 

 good definition and flatness can be obtained with one only. In 

 most cases a slight impairment of definition is observable when an 

 amplifier is used, owing I believe as much to reflection from its 

 surfaces as anything else. But it is not noticeable on many objects, 

 and results are thus obtainable which are not so in any other way. 

 Thus, if the concave doubles the amplification, a 1/2 in. so ampli- 

 fied is not the same thing as a 1/4 in., since (1) it covers double 

 the field ; (2) more light can be passed throught it ; (3) there is 

 far more working distance ; and (4) there is far more penetration 

 or depth of focus. Again, a very low-powerco ncave may be so 

 adjusted (see past papers of the late Dr. Woodward) as to preserve 

 the ordinary working distance at the far longer screen distance, 

 and so keep all the corrections of an immersion lens unaltered. 

 And still again, an amplifier, or one or two amplifiers, give a great 

 range of scale on the screen, at various distances. In brief, while 

 as a rule the unamplified image is best wherever it will give 

 exactly what is desired, results can be got with an amplifier, in 

 many cases, which could not possibly be got without one, especially 

 as regards the size of ohject shown under a given power, or the 

 depth of focus required. 



Pretty good results can be got with the more brilliant opaque 

 objects under a Lieberkiihn, and many objects show beautifully under 

 black-ground illumination. The most precious portion of the 

 parallel beam is of course stopped by the dark disk or spot. To 

 avoid this, I have devised a concave glass cone, which spHts the 

 rays from the centre, and so uses approximately all of them, in spite 

 of the spot or opaque disk. 



Some may wish to have an idea of what can be shown on the 

 screen with the oxyhydrogen light, and how far any special slides 

 are necessary. Where transparency is combined with opaque 

 detail, 1200 or 1500 diameters are easily obtained ; and a flea can 

 be shown about 14 feet long, as sharply and nearly as brilliantly 

 as a painted magic-lantern slide. Where extreme transparency of 

 ground is combined with great opacity of detail, as in a fly's 



