120 OPTICAL PROJECTION 



be done with three, and is a charming effect. Except for such 

 extra effects, and for exhibitors who really use these, and 

 know how to produce them, and can give care and skill to 

 registering their own stock of slides for them, the triple lantern 

 is a sheer waste of money ; and the greater part of those pur- 

 chased are never really utilised. 



The centre nozzle of a tri-unial is kept ' square,' and the 

 whole lantern must be first tilted or adjusted by it to the 

 centre of the screen, and this jet first got in order. Afterwards 

 the top and bottom lantern discs are made to coincide with 

 this, and then their jets similarly adjusted. It must not be 

 forgotten that a triple lantern necessarily uses more gas. 



All that has been said about bi-unials, concerning work- 

 manship and simplicity of form (with however high finish) 

 applies in a still greater degree to triple lanterns. I have seen 

 one, regarded with evident pride by both maker and owner, 

 which was a fair load for a cart, and must be a grievous 

 burden anywhere but as a fixture in some hall or other. It 

 should be remembered that these instruments have at least to 

 be taken out of their cases and put back again. 



65. Triple Dissolving. The chief point to be really con- 

 sidered about a tri-unial lantern, is the system of connections 

 and dissolving that shall be adopted. After a great deal of 

 ingenuity, a single dissolving tap was invented, which by 

 turning a lever to the proper lettered places on a disc, would 

 bring any single lantern or pair into play. Such a tap costs 

 about three guineas, but is not practical, as there is not light 

 to read inscriptions during an exhibition. The only really 

 practical tap of this kind I know of, is known in the trade 

 as Noakes's Triple Dissolver. In this tap there are two sets 

 of holes and two levers : one to ' set ' the tap as required to 

 any pair of lanterns, and the other to do the dissolving. The 

 setting handle can be adjusted in the dark with perfect 

 certainty by touch alone, and the other action is quite as 

 simple ; bye -passes can also be arranged as required. 



