Light.

Manufacturer and Builder 1, 1874

One of the strangest incidents in scientific research is that must important discoveries pass by unnoticed, the accounts of them remain dormant for years in memoirs published either privately or by scientific societies, until a long time afterward the same discoveries are brought out by others as a novelty, and then are fortunate enough to attract public attention for the simple reason that in the meantime the scientific world has advanced far enough to realize the portance of the discovery, while before that time the original first discoverer wan too far in advance of his time to see his labors appreciated. These remarks apply directly to one of our most eminent philosophical investigators, Dr. John W. Draper, who thirty years ago published a work entitled the "Forces which Produce the Organization of Plants." This work was illustrated by engravings made after daguerreotype plates, some of which not only represented the different lines of the diffraction spectrum, (quite recently introduced in spectroscopy,) but also possessed for a scale the wave lengths as the proper indices for designating the different, Frauenhosser lines, and a which now have supereeded the scale which Bunsen and Kirchhoff brought out some twelve, years ago when they first published an account of their spectroscopic researches.

Dr. J. W. Draper discovered also, thirty years ago, groups of lines outside the limits of the line A in the dark red or rather brown extreme end of the spectrum. His son, Dr. Henry Draper, has recently succeeded in making photographs of all the spectral lines, even including those. Thus far it had been accepted, that the red end of the spectrum possessed no actinic power, and that therefore it could not be photographed; but Dr. John W. Draper has recently proved that this error is caused by the fact that the blue end of the spectrum acts chiefly on the bromid and iodid of silver, almost exclusively used by photographers; that the yellow portion, for instance, acts on carbonic acid and the red on outer substances, and that therefore the whole length of the spectrum possesses chemical powers, only different in different regions for different chemical preperations. This view has been verified by Dr. Henry Draper by photographing even the lines mentioned beyond A. He publishes also in the last number of Silliman's American Journal some beautiful photographs of many groups of lines, proving the advantage and fidelity of photography over handiwork, as his plates show details not found in the carefully drawn maps of Angstrom, Kirchhoff, Moscato, and others.