tbey have doubtless much to tell, were their message only legible by us. It has not as yet proved so; but the characters in which it is written are being earnestly scrutinized and compared, with a view to their eventual decipherment. The prodigious advantages afforded by great altitudes for this kind of work were illustrated by the brilliant results of Professor Young's observations in the Rocky Mountains during the summer of 1872. By the diligent labor of several years he had, at that time, constructed a list of one hundred and three distinct lines occasionally visible in the spectrum of the chromosphere. In seventy-two days, at Sherman (8,335 feet above the sea), it was extended to two hundred and seventy-three. Yet the weather was exceptionally cloudy, and the spot (a station on the Union Pacific Railway, in the Territory of Wyoming) not perhaps the best that might have been chosen for an "astronomical reconnaissance."[1]
A totally different kind of solar research is that in aid of which the Mount Whitney expedition was organized in 1881. Professor S. P. Langley, Director of the Alleghany Observatory in Pennsylvania, has long been engaged in the detailed study of the radiations emitted by the sun; inventing, for the purpose of its prosecution, the "bolometer,"[2] an instrument twenty times as sensitive to changes of temperature as the thermopile. But the solar spectrum as it is exhibited at the surface of the earth is a very different thing from the solar spectrum as it would appear could it be formed of sunbeams, so to speak, fresh from space, unmodified by atmospheric action. For not only does our air deprive each ray of a considerable share of its energy (the total loss may be taken at twenty to twenty-five per cent when the sky is clear and the sun in the zenith), but it deals unequally with them, robbing some more than others, and thus materially altering their relative importance. Now, it was Professor Langley's object to reconstruct the original state of things, and he saw that this could be done most effectually by means of simultaneous observations at the summit and base of a high mountain. For, the effect upon each separate ray of transmission through a known proportion of the atmosphere being (with the aid of the bolometer) once ascertained, a very simple calculation would suffice to eliminate the remaining effects, and thus virtually secure an extra-atmospheric post of observation.
The honor of rendering this important service to science was adjudged to the highest summit in the United States. The Sierra Nevada culminates in a granite pile, rising, somewhat in the form
- ↑ R. D. Cutts, "Bulletin of the Philosophical Society of Washington," vol. i, p. 70.
- ↑ This instrument may be described as an electric balance of the utmost conceivable delicacy. The principle of its construction is that the conducting power of metals is diminished by raising their temperature. Thus, if heat be applied to one only of the wires forming a circuit in which a galvanometer is included, the movement of the needle instantly betrays the disturbance of the electrical equilibrium. The conducting wires or "balance-arms" of the bolometer are platinum-strips 1120 of an inch wide, and 126000 of
