490 PROFESSOR PIAZZI SMYTH ON THE 
zodiacal light,” no idea except the visible fact itself is included. But to call it 
the “ Sun’s atmosphere,” is taking for granted a supposed fact which has never 
been proved, and is imagining the body to obey peculiar laws, to which it may not 
really be subject. Moreover, as in the case of a phenomenon which is so extremely 
faint as scarcely to be seen at all, a person may too easily persuade himself that 
he sees it as he ought to see it,—so there seemed to be much necessity for making 
further observations, which though they might prove, after all, to be not entirely 
free from errors of judgment and idea, yet would probably not be affected in the 
same way as those of other observers. 
The circumstances in which I was placed were very favourable, so far as the 
clearness of the sky, the purity of the atmosphere, and the advantage of geogra- 
phical position were concerned; but being engaged in the active duties of a trigo- 
nometrical survey, sometimes on the top of high mountains and sometimes in the 
plains below, the different character of the stations exercised too great an influence 
on the phenomenon to be observed, to allow of strict comparison being made he- 
tween the observations at the various places. But there was at least the possibi- 
lity of being able to determine a good method of making the observations, by en- 
deavouring to reduce to practice some plan by which the results should be expressed 
more in numbers than has generally been the case; and of ascertaining at least 
the degree of accuracy with which observations of place, 7.¢., of AR. and Decl., 
could be made, in more or less favourable localities and seasons. 
I proposed to myself, therefore, to endeavour to determine each night the AR. 
and Decl. of the apex of the light; though the only method which was then avail- 
able, viz., observing the particular stars amongst which the point was situated, 
was only of use when there were large stars close by; since even if there had been 
star-maps to refer to in the desert, to identify the smaller ones, the phenomenon 
to be observed was not one that would bear close and direct investigation. It 
was only after having shut the eyes for some little time, or having turned them 
to some dark part of the sky or earth, that on suddenly directing them to the 
region of the zodiacal light, but not exactly to the middle of it,—it was seen 
of a well-defined figure ; for by looking straight at it, and still mcre by coming 
into contact with any artificial light, the situation of the apex appeared to vary 
many degrees, or could not be decided on at all. At length, therefore, in 1844, 
I made a little wooden instrument with equatorial motion, plain sights, and 
roughly divided circles; which being placed in position in some spot free from 
any artificial light, readily gave the means of determining the object sought. 
Then, by the sort of side glance above described, a good notion of the position 
of the apex being obtained, the plain sights were immediately pointed to the spot, 
the circles read off, and their index error obtained by reference to known stars on 
either side. This was usually done two or three times each night, and the mean 
has been entered in the accompanying table as a single observation. 
