BIBLIOGRAPHY OF IIERSCnEL's WRITINGS. ;j85 



Herschel, W.: Synopsis of thk Wiutixgs or— Conliimcd. 



A. D. Vol. P. 



1805 95 33 These olijccts were observed at a distance of -2407. ^:> iiudn's from tbo 

 mirror of a ten-feet rellecting t(;leseope. It was fuuiid that in tbo 

 telescope a body subtending the niagTiilied angle of 2' ID" could 

 easily bo recognized as round. 

 2d Esi)crinicnt, with small Globules of Sealing-wax. 



34 It appeared that "with a substance not reflecting much light the ma^- 



uilied angle must be between 4 and 5 minutes before we can see it 

 round. 



35 3d Experiment, ivith Globules of Silver. 



36-57 4th Experiment, with Globules of Pitch, Bees-xoax, and Brimstone. 

 38-39 5th Experiment, ivith Objects at a greater Distance. 

 40 6tli Experiment, xoith illuminated Globules. 



40 Spurious DiametePvS ok Celestial Objects. 

 Obserrations and Experiments, with Bemarks. 



41 With stars, the spurious diameters are larger tliaii the real ones, which 



are too small to be seen. 

 The spurious diameters of stars are of dill'erent sizes, and under the 



same circumstances their dimensions are of a permanent nature. 

 The spurious diameters of the stars are differently coloured. 



42 Their spurious diameters are lessened by increasing the magnifying 



power, but in a much less ratio. 

 Magnifying power acts less on tljc large diameters and more on the 

 small ones. When the aperture of the telescope is lessened, it will 

 occasion an increase of the spurious diameters; but this increase is 

 not iiroportional to the diameters of the stars, acting more upon the 



43 small spurious diameters and less upon the large ones. Very small 

 stars, however, lose their spurious diameters, and become nebu- 

 lous. 



The spurious diameter of a star is reiluced by haziness of the atmos- 

 phere. At a low altitude a star makes a spectrum, being coloured 

 by the prismatic power of the atmosphere. 



44 Spurious diameters of terrestrial orjixts, with similar re- 



marks. 

 7th Experiment )('(//( Silver Globules. 



45 8th Experiment. 



The luminous spots or spurious disks of th(> globules were of unequal 



diameters. 

 9th Experiment. 10th Experiment. 



46 11th Experiment. 12th Experiment. 



47 13th Experiment. 14th Experiment. 

 48-49 15th Experiment, ^vith Drops of Quiclsilrer. 



50 [These experiments, from the 7th to the 15tli, inclusive, prove that all 



the remarks made concerning the spurious disks of stars are also 

 applicable to sufficiently small and bright terrestrial objects.] 

 16th Experiment, with black and white Circles. 



51 17th Experiment, with different Illumination. 

 18th Experiment. Measures of sjmrious Disks. 



With drops of quicksilver, the spurious disks were measured by means 

 of distant disks of known diameters upon which they were projected. 

 By covering the mirror with screens of ditferent apertures, and also 



52 by stopping out its center by circular screens of ditl'erent size, it 

 was found that the sizes of the spurious disks were not determined 

 by the quantity of light reflected from the mirror, but rather by the 



