186 Daguerreotype Experiment. 



the other resembles in color, the flame produced by the combustion 

 of an alcoholic solution of chloride of sodium, more nearly than any 

 thing else with which we can compare it. The charcoal points were 

 shifted, each to the opposite pole of the battery, without pi'oducing any 

 change in the color of the light given off by the poles respectively. 

 Other pieces of charcoal were substituted, in the place of those with 

 which this phenomenon was first observed, but the difference in the 

 color of the two images was always present, and did not seem to be 

 connected in any manner with the particular charcoal points employed, 

 but the yellow image was uniformly given by one pole, and the purple 

 image by the other pole of the battery. We are under the impres- 

 sion, that the yellow colored image was produced from the charcoal 

 point, in connection with the positive pole of the battery, and that the 

 strontia colored image came from the negative pole of the battery, 

 though of this no note was made at the time. No attempt was made 

 to ascertain by direct experiments, whether these images possessed 

 a different degree of power or not, in producing an impression upon 

 an iodized plate. The difference in their color was presumptive evi- 

 dence that one image, (that from the negative pole,) possessed more 

 of the chemical rays than the other. But evidence is (we are of 

 opinion) afforded indirectly that such is the fact. The light from 

 both charcoal points made a slight impression on the iodized plate, 

 before they were brought so close together as to unite in forming a 

 general blur ; these two small spots or impressions are nearly opposite, 

 or at each extremity of one diameter of the blur, and without its cir- 

 cumference ; one of them is more distinct than the other. Within 

 the edge of the blur, and nearly in the same diameter with the two 

 spots above named, there are also two impressions, darker and more 

 strongly marked, than is the general impression made by the light from 

 the points. One of these spots is doubtless made by the light from one 

 point, while the other is due to the light from the other point, and one 

 of them far exceeds the other in distinctness. Now the more strongly 

 marked spot without the blur, and the more strongly marked one with- 

 in it, are close to each other on the same edge of the blur, and are 

 doubtless produced by the light from one and the same charcoal point. 

 The two other spots, viz. that without, and that within the blur, which 

 are much less distinct, are close to each other at the opposite extremity 

 of the diameter of the blur, and are also evidently produced by the light 

 from the other charcoal point. 



Yale College Laboratory, June 20, 1842. 



