Page:Philosophical Transactions - Volume 095.djvu/48

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36
Dr. Herschel's Experiments on the Means

half its thickness. It measures ,00237; the angle is 0",206; and half of it 0",103.

With 453,0 I see all the globules of a round form, and can by estimation divide No. 13 into two halves. The magnified angle is here 3' 29",0, but as its diameter could by estimation be divided into two parts, the round form of a globule somewhat less might probably have been perceived, so that the magnified angle would perhaps not have much exceeded the quantity 2' 18",9 that has been assigned before.

After some time the weather became much overcast, and as the globules were placed over a cut hedge, the leaves and interstices of which did not reflect much light, they received the greatest part of their illumination from above. This made them gradually assume the shape of half moons placed horizontally. The dark part of these little lunes, however, did not appear sensibly less than the enlightened part, so that there could not be any thing spurious about them.

By this experiment we find that the telescope acts very well with a high power, and will show ah object subtending only 0",484 so large that we may divide it into quarters of its diameter.

 

4th Experiment, with Globules of Pitch, Bee's-wax, and Brimstone.

I had before objected to sealing-wax globules on account of their dingy-red colour; in the last experiment a doubt was raised with regard to the silver ones, because they were perhaps too glossy. In order to compare the effect of different substances together in the same atmosphere, I put up three