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CH. IX] MICRO-PROJECTION WITH HOUSE CURRENT 285
For example, with direct current of 10 amperes one can accomplish a great deal in micro-projection if the manipulation is skillful. To get equally brilliant results with alternating current would require 30 to 40 amperes of current. The heating is also excessive with the high amperages. (See Ch. XIII, § 768).
If alternating current must be used for projection with the microscope, one should not expect too much, but get as good results as possible by observing carefully the conditions giving good screen images, viz., apparatus in perfect order and alignment on one axis; a good screen and a dark room.
It is not wise, according to our experience, to try to use more than 25 amperes alternating current for micro-projection, and it is better as regards the specimens and apparatus, to be satisfied with the results which can be obtained with 15 to 20 amperes. An arc lamp with carbons at right angles is to be preferred.
§ 416. Centering the apparatus on one axis, separating the elements properly and the conduct of an exhibition are precisely as for the direct current light. The results, however, cannot be made as satisfactory, although, as stated above (§ 412), by care and skill much can be accomplished.
THE PROJECTION MICROSCOPE ON THE HOUSE ELECTRIC LIGHTING
SYSTEM
§ 417. As with the magic lantern (§ 127), the small electric current (4 to 6 amperes) available from the regular house lighting system gives very gratifying results.
Small carbons (6-8 mm. diam.) are employed and either one of the small arc lamps especially designed for the purpose or an ordinary arc lamp with adapters or bushings can be used.
Of course the direct current is much more effective, but even with the alternating current, which is now so common in lighting systems, successful projection with the microscope can be done.
The small carbons form a minute crater, and thus approximate closely to a point source of light, which is the ideally perfect source from the optical standpoint. From our experience this is a