ILLUMINANTS 5 



move the light in all directions. The block almost explains itself. The ordinary 

 arrangement for turning the lime is of course present, and in addition a handle for 

 turning both gases down, when not immediately using the light, which is technicnlly 

 known as the " cut off." The oxygen is completely stopped by this arrangement, 

 and only an exceedingly small amount of coal gas (regulated by a small additional 

 thumbscrew, also shown in Fig. 3,) is allowed to pass on to the lime to keep it 

 warm. 



Underneath the jet is seen in Fig. 3 the stand of which we have spoken. One 

 screw serves to shift the jet from side to side, the other raises it from below 

 upwards, or vice versa, whereas a to-and-fro motion to enable the lime to approach 

 nearer to or farther from the microscope or condenser is obtained by bevelling the wide 

 foot of the stand itself so as it will pass evenly and smoothly through two guides 

 fixed on the base board of whatever apparatus is used. This is a convenience, as 

 the light can easily be shifted from one apparatus to another, as we shall presently 

 show. 



We have found this jet by Beard of sufficient intensity for all purposes, but still 

 it is quite possible one of greater power might on special occasions be desirable. In 

 this case we should recommend either the new jet by Gwyer (about which we shall 

 very shortly speak), or the latest pattern quite recently introduced by Beard, or a still 

 more modern jet by Boss & Co. to which our attention has been drawn whilst these 

 pages were passing through the press. It is needless to point out that these high- 

 power jets use an enormous amount of gas, sometimes up to as much as 10 feet an 

 hour of oxygen as well as of coal gas. In our experience we have compared most 

 carefully the high powder of Beard and the most intense form by Grwyer, and we have 

 found that there is but a small difference in intensity of light between them ; but 

 what exists, shows that the latter is a trifle the more powerful. Beard's, however, 

 has a much smaller bore, and we think burns less gas. 



Messrs. Ross & Co.'s latest jet, to which we have just referred, is shown in Fig. 3a. 

 The stand has several movements, and the jet is exceedingly powerful. We are 

 informed that critical tests endorse the extreme power of this jet. 



The Gwyer Jet, Fig. 4, is another form of mixed gas illuminant and one of great 

 power. Although it has not been very long for sale, it has already won many warm 

 adherents. It is exceedingly well made, a,nd has in our hands, when deahng with it 

 experimentally, produced the most admirable results of the greatest intensity. It is 

 manufactured by Messrs. Willway & Sons, who are a guarantee for its perfection. The 

 firm issue a very neat pamphlet of instructions for working it, and their remarks are so 



