of cadmium, wavelength = 2,753 A.U. but sufficient adjustment is provided to allow for changes 
in wavelength. 
The spark is produced by a 500 watt transformer working from a source of alternating current. 
This is stepped up to a potential of 10,000—20,000 volts, which in conjunction with a suitable high 
tension condenser connected in parallel with the spark gap and secondary winding of the transformer, 
gives a very powerful spark, rich in ultra-violet radiations. At present no improvement has been 
found from increasing the power, as it gives a larger spark, but no increase in intrinsic brilliancy. 
For photography, a camera of special design is provided. It slides by means of a dovetail 
and clamp on to the bedplate of the apparatus. It is designed to take two photographs on one 
plate by means of a simple repeating back, 
The Beck Barnard Ultra-violet Microscope Outfit. 
The outfit consists of :— 
The microscope stand, the bedplate, the optical bench for illumination by visible light, 
including mercury vapour lamp and resistance, collimating lens, 1} in. glass prism, the optical 
bench for ultra-violet illumination, with spark gap, pinhole camera, quartz collimating lens, 2 quartz 
prisms, shields for surrounding illuminating apparatus, interferometer, fluorescent eyepiece, 
three Barnard interchangeable object glass holders, detachable camera and plate holder, and the 
following optical equipment :— 
2 Quartz microscope eyepieces. 
1 Monochromatic 3 m/m. quartz immersion object glass. 
1 Apochromatic 3 m/m. oil immersion object glass. 
Duplex dark ground illuminator and quartz substage condenser. 
Plates of uranium glass. 
Didymium screen. 
Glass trough for filter. 
Patent ultra-violet and high power dark ground illuminator. 
The following lenses are to be recommended in addition for use with the above apparatus :— 
1 Apochromatic 8 m/m. object glass. 
1 Apochromatic 16 m/m. object glass. 
1 Compensating eyepiece, 8. 
1 Compensating eyepiece, 25. 
Price quoted upon application. 
The apparatus as quoted does not include the provision of the necessary transformer, etc., 
required to produce the spark. This portion of the apparatus can be supplied to special order, 
according to the current available, which should be stated when ordering, or when quotations 
are asked for. 
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