Light; a course of experimental optics, chiefly with the lantern . hat when the regulator is intro-duced, and adjusted to a given pressure,that pressure will never vary so long as apressure not inferior is kept up behind gases can thus be adjusted equally toany pressure which the weights at com-mand will enable the bags to keep up tothe end. With such regulators, and trialwith the U-tube, if there is a tolerable pres-sure of gas from the main, the mixed jetcan thus be used with 07ily one gas-bag, whichis a very great advantage, giving even at the pressure of themain (say 2 inches, or i
Light; a course of experimental optics, chiefly with the lantern . hat when the regulator is intro-duced, and adjusted to a given pressure,that pressure will never vary so long as apressure not inferior is kept up behind gases can thus be adjusted equally toany pressure which the weights at com-mand will enable the bags to keep up tothe end. With such regulators, and trialwith the U-tube, if there is a tolerable pres-sure of gas from the main, the mixed jetcan thus be used with 07ily one gas-bag, whichis a very great advantage, giving even at the pressure of themain (say 2 inches, or i inch on each side of the U-tube) abetter light than most blow-through jets. Another advan-tage the mixed jet used in this way has over the ordinaryblow-through jet, is that the oxygen gas lasts nearlydouble the time, or goes twice as far. A single jet may thusbe employed at all times, either with gas from the mainto give with half the oxygen a light equal to that of theblow-through form, or, with an extra bag and morepressure, the full light of the mixed Fig. 4. I] CENTERING THE LIGHT. Ji The lime has to be brought very close to the mixed jet—say ^ of an inch from the orifice : hence the inclinationand a well-finished conical point are of jets are so clumsy and so low in angle, that theycast a shadow on the condensers, standing in theirowri light, as it were. For optical work it is importantthis should not be the case. To avoid it, some makersplace the jet upright; the cylinder, or flat side of a discof lime, being itself inclined at 45°. This is, however,dangerous, the heated gases being reflected off the limedirect to the condensers. In any case the lantern shouldbe warmed up cautiously to avoid cracking the lenses. The limes well-known to opticians as Excelsiors are farthe best. Soft limes are often recommended for blow-through jets, but those named give at least equal, if notgreater, brilliancy, with a smaller radiant spot; and witha blow-through
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