648 
SUMMARY OF CURRENT RESEARCHES RELATING- TO 
pinion coarse adjustment, but without a fine adjustment. The substage, 
which consists merely of an arm capable of being thrown to one side, is 
of the push focussing type; it carries an achromatic dissecting loup, 
which makes, as Mr. Nelson has pointed out,* an admirable condenser. 
A Microscope of this kind is a very serviceable instrument for 
serious work, as a 1/4-in. objective can be easily worked without a fine 
adjustment. It is a capital plan, when using a high power on a first- 
class stand, to have one of these elementary Microscopes on the table as 
well, for it will be found in practice more convenient to move the speci- 
men from the larger instrument to the smaller one, when it is required 
to observe the object under a lower power, than to employ a rotating 
nose-piece, for the reason that a change in power necessitates also a 
change in the illumination, and in altering the illumination much time 
will be lost. # 
Nelson’s Stepped Hackwork (Coarse Adjustment). — Fig. 153 shows 
Mr. Nelson’s new stepped rackwork and pinion as fitted to his Micro- 
Fig. 153. 
scope by Messrs. Watson and Sons.f The little screw above the right- 
hand rack is for the purpose of regulating the amount of “ step,” while 
the two screws in the centre of the pinion regulate the pressure by which 
the pinion is forced into the rack. 
In ordinary rack-and-pinion work, if there is to be no “ loss of time,” 
considerable pressure is needed ; but with this kind of stepped rackwork 
only slight pressure is necessary, “ loss of time ” being impossible if the 
right-hand rack has been properly adjusted by means of the upper screw, 
and then fixed by its clamping screws. 
Method of Enlarging and Deepening the Field of a Compound 
Microscope.* — Mr. R. Forgan exhibited a practical method of enlarging 
and deepening the field of a compound Microscope. The essence of the 
* Journ. Quekett Micr. Club, iv. (1889) p. 77. f Cf. this Journal, ante, p. 261. 
X Proc. Roy. Soc. Edinburgh, May 16th, 1899. 
