JOHN WILLIAM DRAPER. 



and extending from the green to the ultra-red is a strongly-marked 

 region in which the action of daylight has been altogether arrested 

 or removed, the daylight and the sunlight having apparently coun- 

 terbalanced and checked one another ; and (3), a similarly protected 

 region, much shorter, beyond the violet. The phosphorograph, in 

 the absence of extraneous light, shows a shining region correspond- 

 ing to number one of the photograph. But if foreign light inter- 

 venes there is annexed to this region another, including the less 

 refrangible spaces, of decided blackness, broken, however, at a short 

 distance below the red by a luminous rectangle of considerable 

 width, formed by the coalescence of the bands , /5, Y- There is also 

 a similar but smaller region in the violet. In this memoir Dr. 

 Draper notices the rapidity with which the red spectrum rays ex- 

 tinguish phosphorescence. 



The electrical investigations which were undertaken by Professor 

 Draper were much fewer in number than those on light. One of 

 the most important of these was a paper on the electromotive power 

 of heat, published in 1840, in which he discusses the electromotive 

 force developed in pairs of different metals as the temperature rises 

 and gives values for wires of copper-iron, silver-palladium, iron- 

 palladium, platinum-copper, iron-silver, and iron-platinum, obtained 

 with one junction kept at 32 and the other raised either to 212 or 

 to 6G2F. He gives curves of the thermo-electric action of these 

 metals, the abscissas being temperatures and the electromotive forces 

 ordinates, constituting a thermo-electric diagram. In this diagram 

 the curves of iron-palladium and copper-silver are concave toward 

 the axis of abscissas, while those of iron-platinum, copper-platinum, 

 and silver-palladium are convex toward this axis. He observed 

 also that the increase of electromotive force with temperature dif- 

 fered for the different pairs. He calls attention to the anomalous 

 results which are given by pairs into which iron enters, and gives 

 the diagram of a copper-iron couple, the maximum ordiuate of which 

 is at 650 and the neutral point at a temperature at which an alloy 

 of equal parts of brass and silver melts. The paper concludes with 

 several suggestions in regard to the forms which it is desirable to 

 give to the components of a thermo-electric couple. 



In 1834 he studied the action of the galvanic battery and pub- 

 lished an account of some improvements in its construction which 

 his experiments had suggested. In 1835 he repeated the experi- 

 ments of Morichini and Mrs. Somerville on the reputed magnetiz- 



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