406 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
the foot above referred to, objects of large size can be examined. Its 
free extremity receives either a socket for bolding the Microscope or 
pliers for bolding tbe lenses. For this purpose, these pieces are pro- 
vided with a pin, which fits into the hollow extremity of the arm, and 
can be fixed in any position required by means of a clamp-screw. By 
this arrangement the change of the pieces is rendered very easy, and 
the Microscope-tube can be placed vertically, obliquely, or horizontally. 
This last position is very useful when objects placed vertically, such as 
the side of an aquarium, are to be examined. Indices mark the vertical 
and horizontal positions, and also that at 45°. 
The pliers for holding the lens are not, as in other forms of appa- 
ratus, in the exact axis of the arm, but at right angles to it. Owing 
to this arrangement, there is no risk of the nose of the observer coming 
in contact with the arm, and he is not obliged, in order to avoid this, 
to turn his head on one side. There are two pliers, the larger for 
ordinary lenses, the smaller for objectives. One is in front of the arm 
and the other behind, and they can be placed on either side by turning 
the pin fixed to the end of the arm. 
The rotating ring of the arm has on the opposite side another arm, 
which is shorter and is terminated by a brass ball filled with lead. It 
serves to counterbalance the long arm and thus to maintain the stability 
of the apparatus. 
Heating-Lamp with Electric Regulator for controlling the Gas- 
supply.* — In order to prevent the escape of gas after accidental extinc- 
tion of the flame in a lamp intended for keeping up a constant tempera- 
ture, Herren F. and M. Lautenschlager have patented one in which a 
valve is inserted in the supply pipe, and this valve is kept open by 
means of an electro-magnet as long as the lamp burns. If this be ex- 
tinguished, the mercury in the contact thermometer falls until it sinks 
below a wire melted into the thermometer at a suitable place. As this 
wire forms part of the path of the electro-magnet, the current is thereby 
broken, the valve closes, and the gas supply is cut off. 
Polarization without a Polarizer. — We cannot congratulate the 
author of the following note on the originality of the wonderful dis- 
covery he has made. Wheatstone and Brewster have unfortunately been 
before him. We cannot answer for American skies (which no doubt 
“ whip creation ” in polarizing as well as in other effects) but in this 
country at least we fancy that better results would be obtained, when 
no polarizing nicol was at hand, by the simple expedient of using for 
mirror a few glass slips inclined at the polarizing angle. Interference 
figures in crystal sections may often be seen with tolerable clearness 
when the polarization is produced by simple reflection from the work- 
table. Mr. H. M. Wilder says:f — “I have accidentally made a quite 
useful discovery, which I have not seen mentioned before. In order to 
polarize , we put a polarizer (Nicol) beneath the stage, and an analyser 
(Nicol) above the objective (either right next to it, at the end of the 
draw-tube, or above the eye-piece). The selenite comes on top of the 
polarizer. Now I found that the polarizer is not absolutely indis- 
* Zeitschr. f. Instrumentenk., xi. (1891) pp. 73-4. 
t Cf. Engl. Mech., liii. (1891) p. 113. 
