380 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Generally, the instrument, as will be seen, is on the Hartnack model, 
but with an Abbe condenser. The condenser is on an arm with rack 
and pinion, so that it can be instantaneously moved in and out of the axis, 
by racking it down and turning it to the left. The maker claims that 
“ this is a great advantage as against the instruments of other makers 
W’hich have not such a contrivance.” The claim as made is too wide, as 
we have seen German instruments which have had a similar arrangement 
in principle, though it might be more generally applied, as it is often 
very inconvenient to be obliged to alter the position of the Microscope, 
and slide out the illuminating apparatus when it is desired to work 
without the condenser. 
For rapidly changing objectives, the instrument, as shown in fig. 30, 
is supplied with a Fuess clamp, the objective being released by pressing 
the end of the “ tongs ” together against the spring. 
Blackhall’s Simple Microscope with Multiple Illuminator. — In 
this little instrument (figs. 31 and 32) sent us by Mr. W. Blackball, an 
Fig. 31. Fig. 32. 
ingenious device has been made use of for illuminating the object, which 
is fixed on a pin in front of the simple lens. The bottom of the tube, 
in place of being closed by a convex lens, has a “ multiplying glass,” as 
shown in fig. 32, by the facets of which the light is thrown on the object. 
Heyde’s Microscopes for Theodolites.* — Herr G. Heyde has designed 
an instrument intended to unite the advantages of the screw Microscope 
with the convenience of the small Hensoldt scale Microscope. It has 
not generally been found possible to apply the screw Microscope to 
small theodolites, on account of the inconvenience for transport, &c., and 
yet their accurately divided scales deserve a better method of reading 
than either the Vernier or Hensoldt Microscope. 
In the new theodolite M, Mj (fig. 33) are Microscopes with parallel 
wires for reading the horizontal scale H ; they are attached to the arm 
A^, which carries the supports of the telescope-axis. Below A^ is a second 
* Zeitschr. f. Instriimentenk., viii. (1888) pp. 171-6 (3 figs.). 
