of Magnetical and Meteorological Instruments. 323 
board, rather larger than itself, and with a soft wide camel’s hair 
brush kept exclusively for this purpose, apply the above solution 
uniformly and somewhat sparingly to its surface, taking care not 
to leave on it enough to run when the board is held to the fire, in 
which case yellow stains will be produced in consequence of a 
determination of the sulphuret of silver to parts which were too 
much wetted. Hold the paper on the board promptly to the 
fire so as to dry the solution uniformly and rapidly, and leave 
the salts very much on the surface ; care must be taken not to 
scorch the paper. In brushing the paper, in this, as in all subse- 
quent processes, it is well to take pains not to allow any of it to 
run over the edge, to the reverse side, where it leaves unsightly 
Stains. Paper thus prepared, is not affected by light, and will 
keep a considerable length of time, but as it performs best when 
fresh, the inventor recommends the preparation of ouly a week’s 
supply at once. An ounce of solution is sufficient for twelve or 
fifteen slips ; on one occasion a paper of three months old at To- 
ronto, yielded a good curve, but in general they present neutral 
patches to a greater or less extent, if kept too long. 
The next step is to render the paper sensitive. For this pur- 
pose, prepare another slip of wood; secure a slip of the prepared 
paper to this, in the same way as before; exclude daylight, and 
make use of a lantern glazed with red or yellow glass, then 
pour into a capsule about a teaspoonful of the following solution. 
_(2.) Dissolve fifty grains of nitrate of silver in one ounce of dis- 
tilled water; apply it to the paper lightly and carefully, brushing 
first longitudinally, then across ; it is scarcely necessary to say that 
each solution must have its own brush, its own cup, and even its 
Own cloth for drying the cup and brush.* The paper being uni- 
water pressed out of it, by passing a glass rod or piece of tube two 
or three times over it, with gentle pressure. (‘T’o avoid the contact 
of organic matter with the prepared surface.) About half a tea- 
Spoonful of the nitrate of silver solution is then poured on the paper, 
* A small covered box having a place for each cup, each bottle, and each brush, 
Will be found convenient. The cups should be further distinguishable by some differ- 
ence of shape or color, and the brushes marked. 
