188 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1949 
This late-type barrel spiral is an isolated stellar system or, possibly, 
an outrider of the Ursa Major cloud of bright nebulae, and its distance 
is of the order of 5 million light-years. The plate is included to illus- 
trate the resolution of fairly distant nebulae, and the opportunities 
now available for the study of the very brightest stars in stellar 
systems. 
Plate 10, Messier 3 (NGC5272); R.A.=13539"5, Decl.=+28°38’ 
(1950); Apr. 21, 1949; exposure 3 min., made with an aperture of 160 
inches, and a Ross correcting lens; seeing average; enlarged 8X. 
This plate, of a well-known globular star cluster, is included to 
illustrate the use of a Ross correcting lens, placed a few inches in 
front of the plate, to enlarge the coma-free field of the telescope. 
The lens performed well with the 160-inch aperture but, with the 
full 200-inch, it exaggerated the effects of the turned-up edge of the 
main mirror. The provisional mounting of the lens did not permit 
the use of a guiding eyepiece, so the plate shows the successful per- 
formance of the tracking mechanism of the telescope during an 
unguided exposure of 3 minutes. The usable field with this correcting 
lens is more than 15 minutes of are in diameter. 
