140 S. P. Langley—New method in Solar Spectrum Analysis. 
the vicinity of Williamstown, Mass. (Northwestern Berkshire), he 
observes. that the rock of the Taconic range is mainly a “very 
Jine-grained mica slate—a rock which had been called ‘ soapstone 
t,” he adds: “I have 
been able to detect but avery minute quantity of magnesia in 
any specimens I have tried, though I obtained a considerable pro- 
portion of alumina.” 
In a later article (vol. viii, p. 8, 1824) he says: “The Taconic 
Mountain is a huge mass of mica slate.” He also uses in the 
same article the term “talco-micaceous slate” for some portions of 
the rock, but still holds to the result of his chemical trial that the 
amount of tale was very small, and that it was strictly mica slate. 
Art. XX.—A proposed new method in Solar Spectrum Analy- 
sis ;* by S. P. LANGLEY. 
_ No observation of modern Physical Astronomy is more strik- 
ing in its conception, than that which attempts to determine the 
gave experiments of his own, to show that its causes were 80 
numerous and so subtle that it was difficult to be certain of any 
formidable one of its own. I mean, of course, the observation 
of the different wave-lengths of light coming from the east an 
west limbs of the sun, which, owing to that body’s rotation. on 
its axis, have equatorial velocities that together make up nearly 
two and one-half English miles a second. is speed, enormous 
in itself, is most insignificant compared with the velocity of 
light, and this relative smallness constitutes the difficulty i0 
TS neg alana op National Academy, held in Washington, 
+0. R., tome Ixxxii, pp. 761-812. 
