. The microscope; an introduction to microscopic methods and to histology. Microscopes. 4i8 MODELS FROM SERIAL SECTIONS [Ch. XI. multiplied by the amperage used, if the voltage is lowered the amperage is raised proportionally; hence the need of the large wire on the side toward the lamp beyond the transformer where the amperage is increased. § 676. Lamp for 6-volt current. — There are in common use two lamps, one of 72 watts and one of 108 watts. Now as the wattage is the voltage times the amperage, for the 72-watt lamp the amperage with a 6-volt current must be 72 divided by 6 or 12 amperes.
. The microscope; an introduction to microscopic methods and to histology. Microscopes. 4i8 MODELS FROM SERIAL SECTIONS [Ch. XI. multiplied by the amperage used, if the voltage is lowered the amperage is raised proportionally; hence the need of the large wire on the side toward the lamp beyond the transformer where the amperage is increased. § 676. Lamp for 6-volt current. — There are in common use two lamps, one of 72 watts and one of 108 watts. Now as the wattage is the voltage times the amperage, for the 72-watt lamp the amperage with a 6-volt current must be 72 divided by 6 or 12 amperes. For the 108- watt lamp in hke manner the amperage is the watt- age divided by the volt- age, —108 divided by 6 = 18 amperes. This shows at once why the large wires must be used be- tween the lamp and the transformer. If the usual small wires are used the resistance is too great and part of the energy is used up in heating the wires instead of in heating the filament to supply the hght. It is also a good plan to have the wires between the transformer and the lamp as short as possible and not be inconvenient. § 677. Arrangement of the lamp for the large projection outfit. — If the lamp is to be used in the lamp-house instead of an arc lamp for the large projection outfit, it must be centered carefully and put the right distance from the large condenser. The filament takes the place of the crater of the arc lamp and hence should be in the focus of the first element of the condenser, so that the beam between the first and second elements of the condenser will be approximately parallel. If a two-lens condenser is used the lamp filament is slightly within the focus, making the hght slightly diverging between the two lenses of the condenser. Fig. 246. Drawing and Projection Outfit WITH Large Mirror on Separate Drawing Table. For fuU explanation see Fig. 112. Instead of the arc lamp here shown the 6-voIt incandescent lamp can be used for most purposes (§676).. Please note that
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