ATMOSPH KRIC ACTINOM I-'/rU Y 



uliicli sciciicti liuH as yet no jiiiswer ; in>t tliat I lie siiKjcct lias iml, iilifady lu-cii 

 |Im>ii>ii<;1i1v iiivcstiL'ftted, but hcciiUHe in nil the artinoinoliic; iiwiiiirics )>i(i|uis<'(l so 

 fai', siillicicnt caif lius not IxM'ti bestowed upon the separation of tlicniical at-tion 

 from hiininoiis and calorilir cH'ectH, 



'V\h: proeess whicii best shows the incorrectness of I In- nicthods employed 

 her«'tofoit' is ihai of Ab-s^is. I'linscn and lloscoe, \\hi<di drpcnds upon a iiiixtiire 

 of clilciriiic and nf li yd roi;en, exposed (o ihe li|_dil, 'I'lir intensit\' nf (lie clirniii'al 

 action is then estimated by tln^piantity of liy<h<Kdiloric acid formed in a i^iveiL time, 

 oi' rath(!r l»y the diminution of v(»bim(' which necessarily follows. This method 

 has two grave defects. One is that reaction may take jilace from the etVect of heat 

 (piite as W(dl as fi'om that of ehemical rays, and thai ciiiisccpicntlN' it does not 

 H((parate the two ;ictii>ns wliicli it is iniportaut to isolate. The second, niiiih inoi'e 

 serious, defect is this, that the reaction is e.xti'emely exnt licrniic and continues, 

 wlii'n ciiice begun, under llic intlnencc of the heat wliirji ii develops. 'J'here is, 

 t lierefcife, ih> pn ij luil ioiiality l)et\\('en the ;icti\e cause and the eil'ecl it produces. 

 The cans(' Is simply pr<>\ (icali\ c and starts a inerliani-ni, which cuntinues tn work 

 independently, it is true that an effort is made to rednce to a minimnni the work 

 of this mechanism, l>y opeiating only with very small quantities of gas and by 

 multiplying tli(! cooling snrfnces, in such a \va\- tliaf the phenouK'non constantlv 

 re(|iiires a new excitation in oi'der to continue. \'>nl this is not suilicienl to relieve 

 the nuithod of the chai'ge of lacking proportionality Ix'tween cause and effect, which 

 I'cnders the measurements almost illusory, in spile of the care tak<'n by Messi"S. 

 liunsen and Uoscoe to discuss them. 



\\ (• tin<l the same d(!f(H'ts, though peihajis a little less seriously, in the often 

 (employed melliod which depends npon the reduction of ferric oxalate b\' light. 

 Since the lirsl obsei\ation by 1 )ol)ereinei, II. I >raper, Marchand, and (I. Lemoine 

 hav(! studied this icaction. .\s in the preceding case the o.xalatc!, or the 

 eiplivaleiit niixliireof fe|-ric chloride .■iml ox.alic acid, is rc(liiced by the ;iction of 

 heat alone, ami alllioiigh this I'cdiiclicin is slow, it operates as ;i sonrcc i)f error. 

 Moreover, the Tupiid is coloicd and loses its color in proportion as the ]>rocea8 

 continnes. I bnce the conditions of absorption .ire modilied dnrim,' the process 

 and this by u |ilienomenon which is to a certain degree external. I'^inally, the re- 

 liction is still siiHicieiitly exoilieinilc |o ri'ipiiic lli.it lliis properix' should l)e t;iken 

 into account. All these defects have been corrected, so tar as possible, by M. G. 

 i.cmoine, who has for some time lieen making a careful stud\ of the process, but 

 tJie method loses thus (hat neatness and that simplicity which are so desirable. 



The ideal w'oiMd be attained by tin* discoverv of a limpid and trans|)arent 

 rn|nid which would not change while tin* reaction went on, becoming the seat of 



