186 Intelligence and Miscellaneous Articles. 



precisely the same result that is obtained by the direct reduction of 

 .^lish reading. 

 I make the proviso, if the metrical scale is properly Graduated, as 

 there is reason to fear that this is not the case with many double-scale 

 barometers made in this cour.: 



I am, Gentlemen, 



Your obedient Servant. 



William Mathews, Jun. 

 51 Carpenter Road. Edgbaston, 

 November 7. 18 4 



OBSERVATIONS OF THE SPECTRUM OF JUPITER. 

 LETTER FROM FATHER SECCHI TO IE. DE BEAUMONT. 



In my last communication on the spectra of the celestial bodies I 

 gave new observations, which confirmed for the planet Jupiter the 

 existence of special bands due to its atmosphere. I said that I 

 hoped to be able to measure these bands with the greatest precision, 

 and to learn whether or not they coincided with the terrestrial atmo- 

 spheric bands. I can now communicate the result of these measure- 



To obtain them I constructed specially an exce'Jent astronomic 

 micrometer, with a screw having a thread of four-tenths of a milli- 

 metre, the :::^ wires being replaced by a metal plate with a very 

 fine slit. This single slit is used instead of the graduated scale of 

 the spectroscope which I used last year : it is illuminated in the 

 same manner with light graduated at will ; by moving the head of 

 the screw, which is divided into 100 parts, this luminous line may 

 be made to coincide with an obscure band or any given ray ; but as 

 its light would efface the obscure ray if it extended throughout the 

 spectrum, its length was limited so that it only encroached upon it 

 to about one-third or one-fourth of the length of the latter. In this 

 way the micrometric line could be placed in continuation of the 

 spectral ray an astonishing precision. 



The solar rays and that of sodium served as the starting-point for 

 the measurements : the latter was introduced at the moment of ob- 

 servation : the others were served the same day, sometime before 

 sunset, with the same micrometer and spectrometer applied to lienffl 

 large refractor. Great care was taken to fix each time the micro- 

 metric slit on one of the strongest atmospheric rays, to see if they 

 coincided or not with those of Jupiter. In the interval between the 

 observation of the terrestrial atmosphere and that of Jupiter the 

 instrument was left untouched, althousrh it was subsequently observed 

 that this precaution was superfluous. The atmospheric rays were 

 determined by observing the air near the horizon. I also sometimes 

 made use of the moon, which was a little above the horizon ; and 

 then I had the advantage of making one observation on the planet 

 and another on the moon, and then of returning to the planet, by 

 which the control was made more exact. 



The various bands are not equally easy to measure, for some are 



