Page:Philosophical Transactions - Volume 095.djvu/54

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Dr. Herschel's Experiments on the Means

may be seen in my catalogues of double stars, their spurious diameters are lessened by increasing the magnifying power, and increase when the power is lowered.

(5.) It is also proved by the same observations, that the increase and decrease of the spurious diameters, is not inversely as the increase and decrease of the magnifying power, but in a much less ratio.

Nov. 13, 1782. The two stars of the double star 40 Lyncis, with a power of 460 are very unequal; and with 227 they are extremely unequal.

(6.) From this we find, that the magnifying power acts unequally on spurious diameters of different magnitudes; less on the large diameters, and more on the small ones.

Aug. 20, 1781. I saw ε Bootis with 460, and the vacancy between the two stars was 11/4 diameter of the large one. I then reduced the aperture of the telescope by a circle of paste-board from 6,3 inches to 3,5, and the vacancy between the two stars became only 1/2 diameter of the small star.

The proportion of the diameters of the two stars to each other was also changed considerably; for the small one was now at least 2/3 if not 3/4 of the large one.

(7.) This shows that when the aperture of die telescope is lessened, it will occasion an increase of the spurious diameters, and when increased will reduce them.

(8.) It also shows that the increase and decrease of the unequal spurious diameters, by an alteration of the aperture of the telescope, is not proportional to the diameters of the stars:

(9.) But that this alteration acts more upon small spurious diameters, and less upon large ones.

Aug. 7, 1783. I tried some excessively small stars near γ