614 
PROFESSOR ROSCOE ON A METHOD OF METEOROLOGICAL 
The Intensity Tables for strips B and C obtained by graphical interpolation from both 
the above determinations, are those used in most of the observations of daily chemical 
intensity about to be described. The curves of these two last graduations are given 
(dotted lines) on Plate XXVIII. fig. 2 ; and from these curves the close agreement of 
the graduations is seen. 
The fixed strip graduated according to the above method is gummed upon the brass 
drum (M) of the reading-apparatus, fig. 6, care being taken to place a thick sheet of 
white paper between the metal and the fixed strip. In this position it is ready for use. 
III. Method of Exposure and Heading. 
For the purpose of making the observations, standard sensitive paper is prepared, 
according to the directions given on p. 155 of the last memoir, by salting photographic 
paper in a 3 per cent, solution of chloride of sodium, and subsequently silvering on a 
bath containing 12 parts of nitrate of silver to 100 of water. After drying in the dark, 
the paper is cut into pieces 100 millims. long by 10 millims. wide, and each piece gummed 
upon the back of an insolation-band (fig. 4) in the position denoted by the dotted lines, so 
Fig. 4. 
that the lower half of each of the nine holes (5 millims. in diameter) stamped out of the 
paper 10 millims. apart, is filled up with the sensitive preparation. These insolation- 
bands may be easily cut out of white cartridge paper by means of an iron ruler 400 
millims. long and 35 millims. broad, the holes in the paper being stamped out by a 
punch fitting into nine corresponding holes in the ruler. The holes in the paper are 
numbered, and the numbers are repeated upon the band at a distance of 87 millims. 
from each hole for the purpose of subsequent adjustment. 
The insolation-apparatus (fig. 3) consists of a thin metal slide (A) 174 millims. in length 
and 40 millims. wide, with space enough between the sides to allow the paper band (B) to 
pass through easily. A circular opening (C) 10 millims. in diameter is cut in the middle 
of the upper side of the slide, and the marks on the bands are so arranged that the line 
marked No. 1 coincides with one end of the slide when the centre of the hole No. 1 in 
the band coincides with the centre of the opening (C) in the slide. A thin slip of brass 
(E) moves easily over the slide, and when brought into the position shown by the dotted 
lines, effectually protects the sensitive paper from the action of the light. If the slide 
(A) be used alone, the cover (E) can be moved by means of a button placed at the back 
of the slide ; it is, however, more convenient to place the slide upon the stand (G), to 
which a lever handle (F) is attached, fitting into the button for the purpose of enabling 
the observer to cover and uncover the opening with greater ease and exactitude than is 
practicable when the hand alone is used. When the intensity of the light is such that 
