number. Both nssuiiiptions linvc served 11s well in obtnining lnrge niini1)ers of iiiiniericnl ngrccnients. Bfilliknn has proved 1)eyoncl doul,t tlint tlicy are miitunlly esclusivc. \YIiieli we niust choose, JIiIliknn lenrcs opeii. Our coiisolntion, ns lie points Ollt, is t h n t wc h n r ~ n check 011 our postiilntes.
'I'hc last lecture was on the peiietmting radintions of the upper ntniosplicrr. IColilhorstcr lins con- clutlcd that there is 11 rnclintion in the ntIllCJS@l~rC* for wliich tlic absorptioii coeflicie~it of wntrr is o-OC~,";?, wliilst the hnrtlest rays from '1%. 1). I i n w n cocflicicnt 0033. 3lillil;nn fiiitis n rntiirition ~vliicli is very probnblp thnt o1)scrretl 1)y KoliUiiirster. Hal-cvcr, he finds that the rnys nrc only sliglitly IinrtIcr thnn the most penetriiting y-rays. 3lillil;nn also finds thnt tlic rays arch nf locnl origin. A Iiclnvy sno~~storni ciiuses their ~lisiil)l)e~~niuce, ant1 tlicy cut clown t o nearly half hy 0.3 inches of lend. XliUiknn puts forrwrtl 1111 csplrin~ition that the rays nrc due to riidionctirc dust of cosniic origiii settling s l o d y through tlic ntniosplirrc. tlic tlccny 1)cing rnpid enough to nccount for tlie tliniuiishing intensity of thc rnys nppo~iching tlie ci1rtli.s siirfiicc.