18G9.] EDWARDS — MICROSCOPE. 25 



confidence, purchase from the three great makers, Ross, Smith & 

 Beck, or Powell & Lealand, and you will probably be equally 

 satisfied with your instrument. For portability and extreme 

 neatness and perfection you may prefer Powell & Lealand's stand. 

 For rare excellence and brilliancy of illumination you may prefer 

 Ross's lenses, and for general excellency and ready adaptation 

 of accessories, you may give the palm to Smith & Beck. But the 

 diiference is one of taste rather than excellence when all are so 

 good and about equally costly. I must say I have a strong 

 leaning towards the Binocular, the best effects of which I 

 have seen in those made by Smith & Beck, and I do not think 

 their first class Binocular Microscope has been surpassed. 



As great weight is to be avoided, I should prefer the second 

 sized stands of either of these makers to the largest, and the cost 

 of a complete instrument would be about £Q0 sterling. 



I have a word to say to my friend who is already supplied 

 with a Monocular instrument, and it is to the effect that a good 

 Binocular becomes a necessity to the man who has studied its 

 value, and therefore I would advise him to add this great improve- 

 ment to his instrument, which will cost about £3 sterling. 



This is not a mere luxury or toy but an agent of research of great 

 value, in addition to which it possesses the great recommendation 

 of relieving the strain upon the vision which has so often seriously 

 affected the eyes of microscopists. By its aid prolonged inves- 

 tigation can be carried on without fatigue. 



With regard to the discussions which have been carried on in 

 the highest circles of the science in respect of the value of extreme 

 apertures in the object glasses of high power, and the comparative 

 defining power of such glasses as the -h, ^rs, -h, and so, I must 

 say that my experience leads me to rely on the general excellence 

 of the glass rather than upon its angular aperture. Comparing 

 a very fine -h (which is more properly a A) of Smith & Beck 

 with a -fi made some years ago by Mr. Ross, senr., which he con- 

 sidered the finest ^ he had ever made, I have been unable to 

 chose between them. The latter has much less angle of aperture, 

 but such brilliancy and excellency of definition that it appears to 

 me to leave nothing to be desired, and I have yet to meet with 

 the object glass at all a rival to it. Again I have worked with an 

 8 of Smith & Beck which seemed perfection and was of very easy 

 ma lipulation. I think a man who has a first rate glass whether 

 or --L , may be well content. But I never yet saw 



