44 PRACTICAL PHOTO-MICROGRAPHY. 



in fact, on a pressure board four feet by three feet, he places a 

 weight of forty pounds.* Figure 11, representing a jet arrange- 

 ment designed by the writer, requires some explanation. 



The jet is an ordinary mixing jet, but has an extra attach- 

 ment consisting of three cogged wheels worked from the back 

 of the jet by the cross piece and operating two taps, one on 

 the O and the other on the H tube. These tubes are operated 

 proportionally by the equal cogged wheels, so that the light 

 being once arranged at its best, both of these extra taps being 

 full open, the brilliance of the light can be lessened without 

 injury to the quality by simply turning the cross-piece. But 

 the H tap has a "bye pass," so that the hydrogen can not be 

 entirely cut off by this tap, while the oxygen is a complete cut 

 off. The result is that the lime never gets quite cold when 

 the gases are not turned up, and there is no need to light the 

 jet each time after it has been temporarily out of use. More- 

 over, by lowering the gases together the worker saves his eyes , 

 and by turning the extra arrangement entirely down leaving 

 only a glimmer of hydrogen burning, the worker saves his 

 time, his lime and his money. The harder the lime the bet- 

 ter for our purpose, for a large area of incandescence, unequal 

 in brilliance and color, is most puzzling and pernicious. The 

 jet figured is made by Messrs. Newton & Co., of London, 

 but is open to the public, being in no way " protected." For 

 a very brilliant light with a small incandescent area as for 

 work of the greatest delicacy both gases should be put under 

 heavy pressure in bags, or preferably, cylinders. Mr. E. M. 

 Nelson has his gases in iron tanks, and gets a very fine light 

 indeed. 



The writer has on several occasions attempted to work out 

 some medium to replace " limes " which crack at awkward 

 times, and are at all times liable to disintegration through ac- 

 cess of damp. Magnesia pounded very thoroughly for two 

 hours in a mortar with sufficient water to form a paste prom- 

 ised well. " Buttons " were made with the paste, each button 



* Since the introduction of Beard's excellent " Regulator," the writer 

 has given up bags, and uses oxygen from the cylinder, pressure being 

 controlled by the regulator. 



