Attempt to apply instrumental measurement to the Zodiacal Light

                                and revolving about the Sun. 
Cassini's friend M. Fatio, made observations of the 
Zodiacal Light about the same time, as did also M.M. Kirch, 
& Eimmart and M<sup>r<\sup> Derham. 
But the subject was not carried further, until taken 
up by Mairan in 1731: he was rather wild in his notion of 
the manner in which the body was formed, viz., by particles 
thrown off from the Sun in consequence of the rapidity of his rotation; nor was he very happy in his name of the "Sun's 
atmosphere", by which he led both himself and others to reason 
upon it, as if it were proved to be, and actually was of a kindred 
nature with the earth's atmosphere. His conclusions however, 
that the whole of the luminous body was of a lenticular form, 
nearly in the plane of the earth's orbit, somewhat excentric with 
regard to the sun, and endued with a rotation about that 
luminary, seem to be remarkably good. And his opinion, so 
far as the lenticular shape is concerned, is also held by Olbers and 
by Sir John Herschel, both of them observers. 
Olbers in a letter to Humboldt in 1833 says, - "what 
you tell me of the changes of brightness in the Zodiacal Light; 
and the causes to which, in the tropics, you ascribe to such vari=
=ations, has excited my interest the more, because I have been 
for a long time past particularly attentive every spring to 
this phenomenon in our Northern latitudes. I, too, have always 
believed the Zodiacal light to rotate; but I assumed it (contrary 
to Poisson's opinion which you communicate to me) to extend 
the whole way to the sun, increasing rapidly in intensity. The lumi=
=nous circle which in total eclipses shows itself round the darkened 
sun, I have supposed to be this brightest portion of the Zodiacal 
Light. I have satisfied myself that the light is very different 
in different years, sometimes for several years being very bright 
and extended, and in other years scarcely perceptible. I have 
not myself been able to observe the sudden fluctuations in