178 ANNUAL OF SCIENTIFIC DISCOVERT. 



destroyed." The author's experiments, as recorded in the former 

 report, and those now detailed, prove that this conclusion has been 

 formed too hastily. Although there are many absorptive media which, 

 at the same time as they obliterate a particular colored ray, destroy 

 the chemical action of that portion of the spectrum, yet there are a 

 still more extensive series which prevent the passage of a ray of given 

 refrangibilzty, and do not, at the same time, obstruct those rays which 

 are chemically active of the same de-gree of refrangibility. This is 

 particularly exemplified in the case of glasses colored yellow by dif- 

 ferent preparations. With some of these the blue rays are obliterated, 

 the chemical action of this part of the spectrum not being interrupted, 

 whereas in some other examples those rays permeate the glass, but are 

 almost entirely deprived of chemical power. A still more curious fact 

 is noticed in this report, for the first time, of some media which have 

 the power, as it were, of developing chemical action in a particular 

 part of the spectrum where the rays did not appear previously to pos- 

 sess this power. Several glasses exhibited this phenomenon to a cer- 

 tain extent, particularly such as were stained yellow by the oxide of 

 silver ; but one glass showed this in a remarkable manner. This glass 

 was yellow when viewed by transmitted light, but it reflected pale 

 blue light from one of its surfaces ; it obliterated the more refrangible 

 rays down to the green, and rendered the yellow far less luminous 

 than usual. In nearly every case the yellow rays are found to be not 

 merely inactive, chemically, but to actively prevent chemical action. 

 After the spectrum has been submitted to the action of this glass, alt 

 chemical power is confined to this yellow ray. The author has hitherto 

 supported the view that photographic phenomena and the illuminating 

 power of the sunbeam were distinct principles, united only in their 

 modes of motion. He was led to this from observing that where there 

 was the most light there was the least power of producing chemical 

 change ; and that as illuminating power diminished, the chemical phe- 

 nomena of the solar rays increased. The results, however, which he 

 has obtained during the brief sunshine of the present summer, leads 

 him to hold that opinion in suspension. In many of the spectra ob- 

 tained (copies of which will be appended to the printed report) there 

 appears to be evidence of the conversion of one form of force into 

 another the change, indeed, of liyht into actinism or chemical 

 power ; and, again, as in Mr. Stokes's experiments, the exhibition of 

 the ordinarily invisible chemical rays in the form of light. 



INFLUENCE OF SOLAR RADIATIONS UPON VEGETATION. 



A memoir has recently been presented to the French Academy by 

 M. Gasparin, in which he examined the utility of adopting a new in- 

 strument for the appreciation of the part due to solar radiation in 

 exciting the phenomena of vegetation. When we compare different 

 climates, we may observe that the productions of our locality are not 

 in proportion to its average temperature ; we see the olive barren at 

 Agen (France), where the mercury stands in the thermometer at 14 



