332 THE MICROSCOPE AND ITS REVELATIONS. 



preferable; objectives of wide angle being kept for * critical ' investiga- 

 tions upon objects specially demanding their use. In this view he is 

 entirely supported by Mr. Dallinger, whose unrivalled experience in 

 Biological work of the highest kind, entitles his opinion on such a point 

 to the highest respect. See Preface, pp. v., vi. 



MICROSCOPES, ETC. 



Messrs. Watson's New Models. A new form of Large Compound 

 Microscope (Fig. 501) has lately been brought out by Messrs. Watson (of 

 Holborn), the peculiarity of which essentially consists in this, that the 

 horizontal axis on which it is suspended passes through the axial point of 

 the plane in which the object lies; so that by inclination of the body and 

 .stage the source of light remaining fixed, illuminating rays may be 

 made to fall on the object at any degree of obliquity. The mechanical 

 stage is so constructed (by placing the entire movement above the object 

 platform) as to give it a thinness not otherwise attainable with the power 

 of making a complete revolution. The mirror with its frame may be 

 slipped off the swinging arm that ordinarily carries it, and slid into a fit- 

 ting on the foot, on which it can be readily centred so as to reflect light 

 upon the centre of the stage, whatever may be the inclination of the 

 latter. And a further variety of illumination may be obtained by rotat- 

 ing the whole instrument on its foot, the mirror retaining its fixed posi- 

 tion in the centre. The principle of these ingenious arrangements is to 

 give to the stage, and all that is above it, every variety of position in rela- 

 tion to a fixed source of light, instead of varying the position of the light 

 in relation to the object. Experience alone can test its advantages over 

 the old models. 



The above-named Makers have also adapted a 'swinging sub-stage,' 

 not merely to this large instrument, but to a smaller one on the scale of 

 the ' Student's Microscope' of Messrs. Ross (Fig. 43); which is furnished, 

 in addition, with a graduated disk for the precise measurement of the 

 obliquity given to the illuminating apparatus. Having carefully exam- 

 ined this instrument, with the Objectives supplied by the makers, the 

 Author is able to speak favorably of its workmanship; and would desire 

 to add the name of Messrs. Watson to those of whose Students' micro- 

 scopes he has spoken with approval at p. 67. 



Messrs. Swiff s New Students' Microscope. These excellent Makers, 

 having adopted the general plan of the 'Wale' model (Fig. 44), of which 

 the Author has spoken in terms of high commendation, have applied to 

 it a new fine adjustment of their own, which gives to the ring that carries 

 the objective a very delicate and steady movement; * replacing the iris- 

 diaphragm of the Wale model with their own 'calotte ' diaphragm. 



M. Nachefs Objective-carrier. Every working Microscopist has de- 

 sired a ready means of varying his 'powers,' without the trouble of un- 

 screwing one Objective and screwing on another. This difficulty has 

 been partly met by the use of the ' nose-piece;' but this cannot be conve- 

 niently made (at least, in the case of the heavily-mounted English 

 objectives) to carry more than two powers. By Messrs. Parkes, of 

 Birmingham, as already mentioned 53, sliding tubes are substituted 

 for screws; but the use of them requires the withdrawal of the nose of 

 the microscope to a considerable distance above the stage. The attention 



1 See " Journ. of Roy. Microsc. Soc.," Vol. i., N.S. (1881), p. 297. 



