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the extraneous light is easily prevented from interfering 
with the exhibition. 
I have brought for your inspection a contrivance for 
holding the sheet of cardboard in a convenient manner, with 
a few additions, which make this method of observing 
useful to some extent to those who do not possess a 
micrometer. 
The following is a description of the apparatus before 
you : — The cardboard screen is about six inches square, one 
side being perfectly plain, and on the other is drawn a circle 
of about five inches diameter, which is divided by finely- 
drawn lines into 10 equal spaces both vertically and hori- 
zontally. The lower end of the centre vertical line is 
marked N, the upper end S, and at the end of the centre 
horizontal line, E and W, in the reverse of their usual 
positions. This card is made to slide in a groove in a very 
light wooden frame. A thin brass tube is attached to the 
lower edge of the frame, and fixed carefully at right angles 
to the cardboard. The other end of the brass tube has a 
clip which fits the tube of the astronomical eyepiece. (In 
this instance I assume that an inverting eyepiece is in use.) 
The brass tube is bent so that the centre of the clip is ex- 
actly opposite the centre of the card screw. On the clip a 
black cardboard shade of 8 inches square is fixed. This 
shade prevents the direct light which comes through the 
opening in the observatory dome from falling on the pro- 
jected image of the sun. An eyepiece should be selected 
which will show the entire disc of the sun, and the distance 
of the cardboard screen so arranged that when the sun’s 
image is sharply defined it exactly fills the circle drawn on 
the card screen. 
To facilitate this, and to make the necessary alterations 
for the difference in the sun’s diameter during winter and 
summer, there is a sliding adjustment with a ciampiug- 
screw. The value of the spaces on the circle can be calcu- 
