96 
Further details of Weber’s results are given in the German periodical, 
Photographische Mitteilungen, edited by Professor Vogel, at Berlin. 
Tt is worth while to call attention to the fact that during the long 
twilights of northern latitudes in midsummer plants receive an appre- 
ciable quantity of the blue radiations from the sky, while receiving 
little or nothing of the red, or heat, rays. 
MARCHAND’S SELF-REGISTERING CHEMICAL ACTINOMETER. 
A convenient form of registering actinometer is that devised by 
Marchand (1875), which he at first called “ photantitupimeter,” but 
which name he afterwards contracted and modified to ‘“ phantupi- 
meter.” This consists of a vertical graduated tube, closed at the 
upper end, into which there can escape and be measured the carbonic 
acid gas given off by the decomposition of a mixture of solutions of 
perchloride of iron and oxalic acid. By the action of sunshine on 
this mixture, carbonic acid gas is slowly disengaged, and by its accumu- 
lation in the measuring tube gives us apparently a means of deter- 
mining the sum total of the influences of the sun during any period. 
This apparatus was diligently employed for many years by Marchand 
at Fecamp, near Havre, and has afforded him many interesting 
results. 
COMPARISON OF MARCHAND’S AND MARIE DAVY’S RESULTS. 
Radau (1877), in his work on Light and Climate, states that the 
results given by different methods of measurement of sunshine appear 
to differ largely among themselves, but yet there is a certain sim1- 
larity in the figures. The accompanying table shows the results of 
observations by Marchand’s chemical method and by Marié-Davy’s 
thermometric method, or conjugate thermometers, which latter, on 
account of jts convenience, has been widely adopted. 
Total daily’ 2) Total daily : 
chemical Moen deity chenaieal Moen daily 
ore chaln jactinomet- effect, in | actinomet- 
? she ricde-. || cubic cen- |" ‘hic de- 
Month. timeters, mone Month. timeters, ee 
of car- AM ae of car- (Mont- 
ponte acid Saeeas homie acid wee 
(Fecamp, Pa we (Fecamp, f rn 
1869-1872). | 1872-1876). | 1969-1872). | 1872-1876. 
januanyers i eees fe heawee 1.84 | 1DYOn| | PAtuguste sae ees 18.92 41.2 
Mebruary; eas. s2-- --teeee- 3.93 1564||;September soss=- saeco = 13.65 31.8 
Marche ome. Dee 6.44 | 26:0) lkOctober =a 6.86 20.1 
| 
JXy 0) rt Se See ee eee eee Ser 14.10 | 3i20' || NOVem ber’ =--- 222-22 2--- 2.89 12.5 
Maven snene fl eky sake B48 19. 46 | 46f2|| December 22.222 — ses--= 1.80 9.4 
June --.----.--..------.-- 21.04 48.2 Annual average--_- 11.03 | 29.3 
Ch ae ee ee eee 21.41 | 50.6 |) | 
Rolfe 1a] | 
If the atmosphere were not so very different at these two localities, 
we could have hoped to use the monthly ratios of these numbers for 
reducing similar series elsewhere to a common standard. 
a 
