OF MAGNIFIED OBJECTS. 15 



micrographs above mentioned. I have seen pictures drawn by Mr. 

 DalUnger, showing well on a disc about 15 feet in diameter, or in 

 other words magnified 60 times — a pretty good test of the fine- 

 ness of his hnes. These pictures can be clearly projected on a 

 ten-feet disc when using the paraffine-lamp with three wicks, which 

 is employed in the lanterns known as the Euphaneron, the Lucidus, 

 and others. 



Some objects may be directly projected on a disc not exceed- 

 ing two or three feet in diameter, with such a light as this, but 

 good work of the kind can only be done with the best form of 

 lime-light. At present, the production of a steady electric arc 

 involves so much trouble and expense, that it is out of the 

 question. 



By the best form of lime-light, I mean that both gases must be 

 under considerable and equal pressure, the oxygen well washed 

 twice, and the lime so placed that the gas-jet gives no shadow. 

 But, even then, a professional lecturer said to me, " If you are 

 inclined for a great deal of trouble and expense, and very small 

 results, obtain an oxy-hydrogen microscope." I am not the pos- 

 sessor of such an apparatus, but I have been collecting all the 

 information I could obtain on the subject for some years. 



It is usual to make lime-light lanterns of wood, and that 

 should be the case with an apparatus for projecting images of 

 objects. The condenser should be four inches in diameter. The 

 best kind will produce a circle of rays focussing at about 8 inches. 

 The object-holder and objective mount — which is racked — 

 should be in one piece, and capable of being moved backwards 

 and forwards in the tube which carries them. The purpose of 

 this is that the object may be placed at the point of greatest light. 

 This point is also a very hot place, and balsam-mounted objects 

 soon suffer ; but much of the heat may be cut off by a trough 

 filled with a solution of alum, placed in the usual lantern-stage. 

 Ordinary microscopic objectives of a-quarter and half-inch focus 

 are considered best ; but when the objects are large, special 

 lenses of large actual aperture and long focus are required. 



The best surface on which to project the picture is a smooth 

 wall or screen coated with white enamel ; transparent screens do 



