The Art of projection and complete magic lantern ... - Yesterday Image

;128For dynamo currents as used at the present time there are several lampsmade, and known as " projectors " and are comparatively small in size,certainly the best is the Brockie Pell, costing fifteen guineas, it is afocus keeping lamp, with the carbons at an angle of 40"' it is verysimply constructed and made adjustable from 7 to 15, or 10 to 20amperes of current, this must be stated at the time of ordering, a littleexperience is needed on the part of the assistant to become familiar withit for optical projection, as it is not the usual Brockie Pell lamp.Stand.—Means must be provided for focussing and adjusting thearc on the condenser and for microscopic work this is required to thegreatest nicety, the most minute movement is sufficient to throw theilluminant out of the plane of light.For bringing about the three necessary movements a mechanicalstand is constructed in a most solid and substantial manner, no backlash or loose parts being permitted as the least unsteadiness on the partof the lamp is fatal for microscopic purposes. The bottom pinion givesa quadrant movement for centreing the lamp in a horizontal position,on the central rod is cut a coarse thread which on being turned raisesor lowers the rectangular levers, giving the perpendicular movement,and the top pinion moves the lamp to and fro to the condenser, each andevery motion is thus fitted to the lamp and enables the centreing of thearc to be brought about in the most perfect and easy manner, whichis not obtainable under any other condition.When will electric light be used in the lantern forgeneral use?—This is a frequent question, and no very easy one toanswer, when electricity takes the place of house gas, and a current isavailable, in as simple a form as gas now is. An arc or incandescentlamp, cannot be attached to a current and switched on as we connectrubber tubing to the gas burner. The lamp must be made to suit thecurrent, or the current to suit the lamp, and this is not done withoutexpense and adjustment, and often with a great loss of power. But inthe case of the lantern being a fixture it is not a very difficult arrangementeven then the results are not comparable with a high grade mixed gas jet.The exhibition at the Crystal Palace recently, fully bore this out, and agreat deal of faith was necessary to bring the mind to believe that thelight was so many times more powerful than the best chamber jet. Foranything but microscopic demonstrations the light is very trying anduncertain, a flat and clear disc as with lime light, is not to be dependedupon, and in some of our institutes where an electric lantern is fixedit is quite an infliction when the lamp blinks, to expect carbon to burn