150 REPORT—1850. 
than once to a set of rays acting in some respects like heat, and at the same 
time exhibiting chemical power, it appears necessary that the mode of ascer- 
taining the positions of the points of maximum calorific power should be de- 
scribed. 
Paper being blackened or strongly coloured, is stretched on a frame, so 
placed that a well-defined luminous spectrum is thrown upon its uncoloured 
side. ‘This is then washed over with alcohol or ether, and the points of greatest 
heat are shown by the rapid evaporation which takes place. After a few 
minutes a whitish spot begins to appear considerably below the red raygwhich 
increases in breadth until it equals that of the luminous spectrum, and in 
length till it forms a long appendage exterior to the spectrum, and extends 
moreover within it and beyond the mean yellow ray. By applying a second 
wash of alcohol or ether, thermographic spots are produced still lower than 
the first heat spot, which show a very remarkable and unexpected extension of 
calorific radiations. The want of continuity in the calorific spectrum is its 
most striking phenomenon ; it consists of four distinct patches, extending to 
a distance below the luminous rays equal to the whole length of the spectrum, 
and a prolongation through the luminous rays up to the end of the violet rays. 
The parathermic rays can scarcely be said to have a defined place amid the 
calorific radiations, but they are usually most strongly manifested in the red 
rays. In this part of the Report it appears likely to prove useful, if we give 
a list which shall as correctly as possible exhibit most of those bodies which 
have been shown to be susceptible of chemical change under the influence 
of the solar radiations, distinguishing the date of observation as far as it can be 
ascertained, and the name of the earliest observer. Although every care has 
been taken in examining authorities, it is not improbable that some errors of 
dates will occur,—but it is hoped they may be few and trivial,—the date of 
publication always being given as correctly as it can be ascertained. 
SILver. 
LAE FSS) RE aR estes IDI. ir ἐὺ Rigel: ee ee 1801 
(photographically employed) ...... Wedgwood and Davy 1802 
—— with organie mattéef-............. J. F. Herseel 777.2. 1839 
with salts of lead................ J. F. Hersehel .:.... 1839 
Chloride of. P2205 Pes... 6, Wi. Scheme sate ἘΠῚ 77 
-—— (photographically employed)...... Nee wie AST ; 4 
darkened, and hydriodic salts ...... Fyfe, Lassaigne...... 1839 
Iodide of (photographically used) ...... ἐν πο μῆς ἘΌΝ ene 
with ferrocyanate of potash........ Hunt.............. 1841 
—— with gallic acid (Calotype)......... Talbot) (29.022 «tee - 1841 
—— with protosulphate of iron (Ferrotype) Hunt.............. 1844 
with iodide of iron (Catalysotype) .. Woods ............ 1844 
Prummide! af!) is ἢν ἔπ ταν DF PY EY τὺ Bayard ἢν sleet -. 1840 
Pluoride ΘΕ: τς στιν έτη, YO BIA bees Channing ..... .... 1842 
Muieretypee cs: as) Sess eeid ads ose ee. Hunt. : 5.01 Fm 1844 
OMIABIGERT Heth, Ui eek Seed ἐλλλῤρειςιςς Davy: ck Sean ae 1803 
With :amimomian τιν: 00) e328) oer. Uncertain. 
Phusphate:of ctrigeds 000s estes oo Byfe ose RR, ea 
Tartrate—Urate—Oxalate—Borate, &c... Herschel............ 1840 
Ben ZOAtes OR τον ec va. 2. va Meee ee ee 1844 
Barmiates οὗν ou ees nd... so ΠΕ ν᾽ ΣΝ 1844 
Palmindtes Of is... ao Sema yeas is ay, Dow τ Ὁ at os See, aed? 
