Page:Philosophical Transactions - Volume 095.djvu/72

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Dr. Herschel's Experiments on the Means

Oct. 8. If the appearance resembling the spurious disks of small stars, which I see with 410,5 in Mr. Harding's asteroid, should be a real diameter, its quantity then by estimation may amount to about 0",3. This judgment is founded on the facility with which I can see two globules often viewed for this purpose.

The angle of the first is 0",429, and of the other 0",214; and the asteroid might be larger than the latter, but certainly was not equal to the former.

With 496,3, there is an ill defined hazy appearance, but nothing that may be called a disk visible. When there is a glimpse of more condensed light to be seen in the centre, it is so small that it must, be less than two-tenths of a second.

To decide whether this apparent condensed light was a real or spurious disk, I applied different limitations to the aperture of the telescope, but found that the light of the new star was too feeble to permit the use of them. From this I concluded that an increase of light might now be of great use, and viewed the asteroid with a fine 10-feet mirror of 24 inches diameter; but found that nothing was gained by the change. The temperature indeed of these large mirrors is very seldom the same as that of the air in which they are to act, and till a perfect uniformity takes place, no high powers can be used.

The asteroid in the meridian, and the night beautiful. After many repeated comparisons of equal stars with the asteroid, I think it shows more of a disk than they do, but it is so small that it cannot amount to so much as 3-tenths of a second, or at least to no more.

It is accompanied with rather more nebulosity than stars of the same size.