Transit of the Shadow of Titan. 53 



so great, that, excepting about the time when the ring presents 

 its edge to the sun — once in fifteen years — the apparent paths 

 of the more distant satellites are ellipses open enough to carry 

 them and their shadows clear above and below the ball, while 

 the specks cast by the nearer ones would be imperceptibly 

 minute. Consequently, the records of such ' phenomena are 

 very few, and will naturally relate to the shadow of Titan, the 

 6th (reckoned outwards) and largest satellite, whose diameter, 

 about three-fourths of a second, according to Struve, con- 

 siderably surpasses that of the others. Sir W. Herschel was 

 the first to perceive a transit of this shadow, 1789, Nov. 2, 

 and notwithstanding his gigantic instrumental means, he does 

 not appear to have repeated the observation. 1833, May 7, 

 Gruithuisen, who had been watching the ring from March 27 

 with a 4-inch Frauenhofer achromatic, and had found the knots 

 of light gradually decrease, and at length disappear together 

 with it, says, " I saw, almost in the position where Schroter 

 placed his two knots in the eastern, now not visible, ansa, two 

 satellites, of which the nearest cast its shadow close upon 

 the shadow of the ring, which I at first was inclined to hold as 

 the shadow of a knot in the ring. I saw besides, at a greater 

 distance, the 6th and 7th satellites, to the "W. of the former 

 ones/' This last expression seems not very intelligible; however, 

 there can be little doubt from his aperture that he mistook the 

 names of these two latter ; and as little, that it was Titan whose 

 shadow he saw. 1848, Sept. 20, Schwabe, the great observer of 

 the sun, says that he perceived with the same kind of instrument, 

 upon the very narrow line of the shadow of the ring, between the 

 centre and the W. limb of Saturn, an excessively minute black 

 point; but he does not refer it to the shadow of a satellite; 

 and possibly this, and even Gruithuisen's observation, may have 

 related to one of those curious irregularities in the shadow of 

 the ring which have been remarked by Schroter, Lassell, and 

 De la Rue. If so, Herscher's observation must have stood alone 

 till the present year, for Dawes sought in vain to recover the 

 phenomenon at the last disappearance of the ring in 1848 and 

 1849. During the present season, however, several persons, 

 led on, as was fitting, by that most clear-sighted and accurate 

 observer, have been more successful. He saw it first, April 15th, 

 with his magnificent 8J-inch Alvan Clark achromatic. Mr. 

 Lockyer, of Wimbledon, caught the next transit on May 1st. 

 The following one, on May 17th, was witnessed by several ob- 

 servers, and as I was fortunate enough to be one of the number, I 

 have thought that a brief account of its appearance might not 

 be without some interest. I had entirely lost sight of Dawes's 

 announcement of the transit for that evening, and turned my 

 telescope on Saturn, solely with a view of ascertaining whether 



