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POPULAR SCIENCE REYIEW. 
ASTRONOMY. 
The Sun’s Rotation Measured with the Spectroscope. — We have to record 
the most remarkable achievement yet effected with the spectroscope, 
though involving no discovery, at least no new result which can as yet be 
regarded as demonstrated. It will be within the knowledge of our readers 
that Secchi, having failed to recognize the effect of the sun’s rotation by the 
spectroscopic method of measuring motions of recession and approach, 
expressed doubts as to the validity of the method itself. These were partly 
based on an erroneous estimate which in some inexplicable w T ay Secchi had 
formed respecting the actual rate of the sun’s rotational movement at the 
equator, this rate in reality amounting to only a small fraction of Secchi s 
estimate. Huggins also failed in obtaining spectroscopic evidence of the 
solar rotation, though he used a spectroscope made by Browning for 
Spottiswoode, (the only one of the kind ever made), on a plan devised by 
Proctor (the automatic battery S-shaped and twice-acting), giving a dis- 
persive power equal to that of nineteen equilateral prisms of flint glass. The 
observers at Greenwich have not as yet announced the final results of their 
attempt to measure the sun’s rotation spectroscopically, though from the gene- 
ral statement made by Sir G. Airy it would seem they have successfully dealt 
with the problem. In the meantime it has been mastered by Professor 
Young, of Dartmouth College, Hanover, N.H. Employing one of the 
marvellously effective ruled plates, made by Dr. Rutherfurd, which give 
diffractive spectra of singular purity, he has succeeded in unmistakably 
recognizing the spectroscopic effects of the sun’s rotation. He regards his 
instrumental means with so much confidence that he relies even upon the 
difference between his results and those due to the direct measurement of 
the solar rotation. He finds the sun’s atmosphere to be travelling some- 
what faster than the visible solar surface. We are not sure that his confi- 
dence in this particular detail of his results is justified by the performance 
of his spectroscopic combination in other cases. The difference of rate, 
about ten miles per minute, seems too small to be measured in this way. 
But, in any case, it is satisfactory to find that a motion so small as that 
due to the sun’s rotation, about one mile per second (or a difference, for 
opposite points of his equator, equal to about two miles per second), can be 
recognized by the spectroscopic method, as this enables us to regard with 
considerable confidence the measurements of stellar motions of recession and 
approach, amounting, as these often do, to twenty, thirty, or even so many 
as fifty miles per second. 
Spectroscopic Measures of Motion at Greenwich. — The Astronomer 
Royal, in communicating the results of measurements of star motions, 
comments on objections raised by Professor Secchi. These are on the whole 
satisfactorily disposed of. Indeed some of Secchi’s objections indicate a 
very imperfect acquaintance with the rules for determining the value of 
results obtained from a series of measurements. The measures cf star motions 
agree on the whole fairly with those obtained by Huggins. Measures of the 
displacement of lines in the spectrum of the moon and Venus have been 
