ACADEMY OP SCIENCES] BIOGRAPHY 5 



Friday being my night with the 36-inch telescope, after observing Mars and measuring the positions of 

 his satellites, I began an examination of the region immediately about the planet Jupiter. At 12 o'clock as 

 near as may be, to within a few minutes, I detected a tiny point of light closely following the planet near the 3rd 

 satellite which was approaching transit. I immediately suspected it was an unknown satellite and at once 

 began measuring its position angle and distance from the 3rd satellite. On the spur of the moment, this seemed 

 to be the only method of securing a position of the new object, for upon bringing the slightest trace of the planet 

 in the field the little point of light was instantly lost. 



I got two sets of distances and one set of position angles, and then attempted to refer it to Jupiter, but 

 found that one of the wires of the micrometer was broken out and the other loose. Before anything could be 

 done the object rapidly disappeared in the glare of Jupiter. From the fact that it was not left behind by the 

 planet in its motion, I was convinced that the object was a satellite. A careful watch was kept at the preceding 

 limb of the planet for the reappearance of the satellite, but up to daylight it could not be seen. 



Though positive that a new satellite had been found, extreme caution suggested that it would be better to 

 wait for a careful verification before making any announcement. 



The following night with the 36-inch belonging to Professor Schaeberle, he kindly gave it up to me, and 

 shortly before midnight the satellite was again detected rapidly leaving the planet on the following side. That 

 morning I had put new wires in the micrometer, and now began a series of careful measures for position. As I 

 have said, the satellite was so small that no trace of Jupiter could be admitted into the field for reference in the 

 measures. It was necessary, therefore, to bisect the satellite, with the planet out of the field, and then by 

 sliding the eyepiece bring the limb of Jupiter into view and bisect it. This method did not permit any measures 

 from the polar limbs of Jupiter. Following the satellite thus, it was seen to recede from the planet to a distance 

 of some 36" from the limb, when it gradually became stationary. Remaining so for a while, it began once more 

 to approach the planet and rapidly disappeared in the glow near the limb. The measures, repeated as rapidly 

 as possible, thoroughly covered the elongation and gave the means of approximating to its period. 



The following morning a telegram was sent out announcing the discovery. Subsequent observations have 

 thoroughly confirmed the discovery. 



On account of its extreme closeness to the planet it is difficult to say just what its magnitude is. Taking 

 everything into account, I have provisionally assigned it as thirteenth magnitude. I hope to be able to settle 

 definitely this question by observing some little star near Jupiter, and then afterwards determining its magnitude 

 when the planet has left it. Until this is settled, any estimate of the actual size of the satellite must be the merest 

 guess, but it will probably be found to not exceed 100 miles in diameter, and perhaps less than that. 



After the first few observations I inserted a piece of smoked mica in the eyepiece, and using this as an occult- 

 ing bar, the measures were made with ease and accuracy. Careful measures thus made from the polar limbs for 

 the Jovicentric latitude of the satellite show that its orbit lies sensibly in the plane of Jupiter's equator and that 

 consequently the satellite is not a new addition to the Jovian family, since it would doubtless require ages for 

 the orbit to be so adjusted if the object were a capture. 



The reader will note from this extract the element of independence which was a character- 

 istic of Barnard's discoveries. He perceived with a sort of intuition that this was probably a 

 new satellite; in fact, he was convinced of it by his brief observations on the first night. His 

 exercise of great care in making no premature announcement was also characteristic. He, 

 furthermore, was quick to realize that it would be a matter of general interest whether the 

 satellite had been newly acquired by Jupiter, and his measurements to decide this point were 

 made a few evenings later. We also see an illustration of his readiness to adapt his observing 

 methods to difficult circumstances in providing a piece of smoked mica for occulting the bril- 

 liant planet. His scientific caution and ingenuity are illustrated by his proposal that the mag- 

 nitude of the object should be determined by comparison with some star of about the same 

 magnitude which some night would lie near the planet's position and thus afford a reliable basis 

 for an estimate of brightness. 



This first addition to the family of Jupiter, which had received careful telescopic observation 

 for nearly three centuries, brought to Mr. Barnard instant recognition as an observer of the first 

 class. The Lalande gold medal of the French Academy of Sciences was awarded to him a few 

 months later for this notable astronomical feat. Professor Barnard followed this satellite with 

 very careful micrometric measurements for many years after its discovery, seeking to improve 

 our knowledge of its orbit, and he published 14 papers covering his observations of elongations, 

 nearly all of them in the Astronomical Journal. The difficulty of observing the object was not 

 because it was so faint, but because of the brightness of the planet. Quite good conditions of 

 seeing were always necessary for observing it, even with the large telescope. So far as is known 

 to the writer, the fifth satellite has never been photographed, and the smallest aperture with 



