409 3670 4 ' 0

It will be seen that III is larger than IV, and I is larger than II, which is the same order of size hitherto found by the best observers. But a somewhat striking fea- ture of the table is the reduction in the size of 1 and 11, which are found sensibly smaller than has been indicated by the result of previous observers. Whether this relative shrinkage of the two smaller satellites is due to systematic errors, is a question which must be left to future research, but as the satellites in this work generally presented a small

T a b l e V. D i a m e t e r s o f J u p i t e r ' s s a t e l l i t e s , 1900, o b s e r v e d a t W a s h i n g t o n .

In spite of all the care which can be taken, con- siderable uncertainty still attaches to the real diameters of all these satellites. Their discs are small, and therefore easily disturbed by the smallest atmospheric irregularity, while the large disc of Jupiter presents a steady and well- defined limb. This doubtless accounts for the somewhat perplexing fact that a large diameter bounded by the limbs of Jupiter can be much more accurately measured than a small one bounded by the unsteady limbs of the satellites.

Wash. Mean Time I! Observed Diameters I! Diameters reduced to

At a place whose coordinates for 1855 are R A . = 2 ah 4m6 Decl. = + I 3" 38'

there is a star not included in the BD. whose variability has hitherto escaped notice. It was first Seen by me either in September or in October of last year. I did not then estimate its magnitude exactly, but contented myself with noting that

May 1 2 1 4 1 0 ' 1 0.61 1 7 1 2 2 0 0 . 7 1

8 I I 10

14 8 45 I .oo '5 8 3 0 0.15 1 6 8 2 5 '1 0.80

2 8 8 1 0 0.67 30 8 5 I 0 . 1 6

both 9m5 according to the BD., 4863 is really om4 fainter, and 4865 (which is AG. Leipzig I 8855) om4 brighter, than that magnitude. On 1899 Nov. 6 and 1900 SePt. 2 it Was invisible in a ginch refractor, although 1 could see a 10m2

star not contained in the BD. whose Place for 1855 is 2 Z h 4416 + 13" 5 1 ' ; but On the Int ofthis month it was again

0.80

0.77 0.70

0.62 eclipse

0 .80 0 . 6 0 0.68

0.88 0.62 0.65 0:55 0 5 5

o x 2

I .oo

I O 5 1 x . 5 2 1.37 0.59 1 . 2 6 1 .37 0.67

1 . 5 5 1 . 5 2 0 .48

1 . 5 6 1.48 0.76

1 . 7 8 1 1 . 5 7 0.10 1.63 I 56 1 . 0 9

1 . 7 2 1 . 6 0

1.49 1 . 2 1 I 0.58 1 . 5 0 1.57 10.57

j ( -

1.31 1 1:33 0 .89

1.63 1 1 . 6 2 'I z:;y :::: 1 1.42 I/ 0 . 5 4

1 .40 0.66

0.59 1.41 1 . 5 8 ' 0.62 0 .60 1 1.61 1 1.44 11 0 . 7 1

0.67 0 .64 0.58 0 . 5 2

0 .68 0 .68 0 .53 0 .60 0 . 8 9 0.78 0 . 5 5 0 . 5 8 0 . 4 9 0 . 5 I

0 .54 0 5 5

-

1.23 1.27 I .05

1.24 1 .29

1 . 2 5

1.33 1.39 1.57 1-45 1.16 1.53 I .46 1.43 1.48

Nearly perfect seeing

1 . 1 5 Perfectly round, no markings

Sat. III about of08 larger in dia- [meter than IV

Sat. I is xo percent larger than II

I .42 round, limb sharp I 45

1 .31 - I - '

U. S. Naval Observatory, Washington, D. C., I900 Aug. 1 5 .

New Variable Star in Pegasug.

T. r. 7. See.