. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. electricmicroscopo on p. 209. This, as an optical radiant, is far thebest I am acquainted with ; and up to this date is, I believe,still the only focus-keeping regulator-lamp whose carbonsoccupy the proper inclined position It is extremely port-able, steady upon its base, very simple in mechanism, andits cost is only fifteen pounds. It is not the lamp usually u 2 164 OPTICAL PROJECTION called the Brockie-Pell, but of much simpler construction ;and the same lamp can be adjusted from about 7 t
. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. electricmicroscopo on p. 209. This, as an optical radiant, is far thebest I am acquainted with ; and up to this date is, I believe,still the only focus-keeping regulator-lamp whose carbonsoccupy the proper inclined position It is extremely port-able, steady upon its base, very simple in mechanism, andits cost is only fifteen pounds. It is not the lamp usually u 2 164 OPTICAL PROJECTION called the Brockie-Pell, but of much simpler construction ;and the same lamp can be adjusted from about 7 to 15, orfrom 10 to 20 amperes of current, according to its size. Ihave seen it work for two hours without a single blink. The effect of the inclined carbons is shown in fig. lower carbon is still set in front of the upper or positivecarbon, according to the length of arc. This brings thecrater considerably to the front of the carbon, while theIncandescent portion of the negative carbon is behind, andinvisible from the front. Hence the radiation to the condensers is reduced, as shown in Fig. 88 to that from the crater, whilethat crater radiates muchmore directly and powerfully ;the general result being, notonly the one radiant point,but that of so much greaterpower, that a lamp whichwould usually be called of2,000 candles power, gives tothe condensers at least 3,000in proportion. The gain inall microscopic and high-classoptical work cannot be over-rated. The management of this lamp is very simple. The uppercarbon, first set by experience the proper distance behind theother, is pushed down by hand till it just touches the lowerone without pushing that down ; as the current when switchedon must draw it down a small distance in the usual manner byan electro-magnet, and so strike the arc. The position as toheight of the point of the lower carbon, and therefore of thearc, can be adjusted within considerable limits. The currentwill first have been ascertained, at least ap
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