OP AIMS AND SCIENCES. 299 



XVI. 



OBSERVATIONS ON JUPITER. 



By L. Trouvelot. 



Presented March 9, 1881. 



In the year 187G, a seines of observations on the planets Mercury, 

 Venus, Mars, Jupiter, and Saturn was undertaken with the intention 

 of following each one of these bodies for as many years as necessary 

 to study them on every point of their orbit, in order to arrive at a 

 better knowledge of their 2Jhysical constitution and meteorology. The 

 plan then formed was to make at least one observation and a drawing 

 of each planet on every favorable day, whenever the object would be 

 so situated that it could be advantageously observed. So far, this 

 plan has been carried out, and over 1,500 observations, accompanied by 

 1,000 drawings, have been made. 



It is my purpose in this paper to make as brief a statement as possi- 

 ble of those portions of my observations pertaining to the rotation of 

 Jupiter, and the great red spot which made its appearance upon its 

 surface in the year 1878; reserving the rest for publication whenever 

 means shall be found for printing the plates in a suitable manner. 



The facts here recorded were selected from the 591 observations 

 and 567 drawings of the series made during the last five years. 



The year 1876, the first of my regular and systematic observations 

 of Jupiter, was one of extraordinary disturbance, and nothing ap- 

 proaching it has since been witnessed. The changes were so rapid 

 that, save in one case, no spots or markings could be recognized the 

 day, nay, sometimes even the hour, after they had been observed. 

 Since that time, the surface of the planet has been remarkably quiet, 

 only an occasional change taking place. During the last four years 

 some of the markings have been very persistent, and remained in sight 

 for years, with but very little apparent change. 



Mark A. 



In one case only, as has been said above, was a spot recognized in 

 1876. This object, first seen on May 19, was recognized ou May 21, 



