THE DISCOVERY OF THE SUN SPOTS. 681 



preceded by condensed gaseous waves. We can not, therefore, 

 doubt that the cushion of greatly compressed air in front of the 

 projectile causes considerable delay in its progress, and conse- 

 quently a great heating of the ball. We know that this takes 

 place with aeroliths which become incandescent and burst in fly- 

 ing through our atmosphere. 



Melsen's experiments led me to suppose (in 1874) that the ob- 

 struction and heating of a projectile passing through the air 

 might be notably diminished by driving a narrow and slightly 

 conical channel through the ball and slipping into it a metallic 

 obturator to fit it. " In this way," I said, in my lectures on ther- 

 modynamics, " the ball might be discharged without letting more 

 gas escape than usual ; once out of the chamber, it would con- 

 dense the air in front of it, while the air behind it would be ex- 

 tremely rarefied. A difference of pressure would immediately be 

 produced sufficient to force the conical tampon out of the projec- 

 tile, and after that there would be no more projectile- air pres- 

 sure." Under these conditions, I said, the velocity of projectiles 

 could be kept up for much greater distances, and the heating 

 would be considerably less. I was not so situated that I could 

 verify these views by experiment ; but the principle was applied 

 about two years ago in Germany, in the Hebler Kruka ball, the 

 axis of which is pierced with a small cylindrical channel, en- 

 larged behind so as to be funnel shaped, and closed with a small 

 plug the very device I had imagined twenty years before which, 

 when fired from a cannon, behaved just as I supposed my perfo- 

 rated ball would do. Translated for the Popular Science Monthly 

 from, del et Terre. 



THE DISCOVERY OF THE SUN SPOTS. 



Br M. A. LANCASTER. 



SPOTS or groups of spots were seen more or less distinctly 

 upon the sun previous to the invention of the telescope. The 

 observations are described under various forms, first among 

 which may be mentioned obfuscations or obscurations of the sun. 

 At other times they were believed to be passages of Mercury in 

 front of the sun, as in 807, a date mentioned by the historians of 

 Charlemagne, and on the 28th of May, 1607, when even Kepler 

 was deceived. In 859 Alkindi thought he observed a transit of 

 Venus ; but the black object he saw on the sun's disk was only 

 a spot large enough to be perceived by the naked eye. 



Observations of obscurities or spots on the sun have been 

 made in China at different epochs, the most ancient one dating 

 from the year 301. Between that date and the beginning of the 



