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star to an extensive spectograpliic ill^•estig•ation in tiio winter months 

 of J9()i— 2 and 1902—3, and, troin llie 42 [)Ialos ohlained, drew 

 the foUowinii; conclnsions. 



The «pectrnni contains chiellv tlic lines of livdruuxMi and heUnni ; 

 besides a few l)eU)nging to siiicium, nnxgiiesinni, ealciuni. 



The caieiiini line at X 3934 (con'espondinii to A' of the solar 

 sj)eetrnin) is extraordinarily weak, hnt almost iierfcctly siiai-p; all 

 the otlier lines (nineteen in mnnher) ai'c \ei"y dilfnse and dim, often 

 appear crocked and nnsynimetricai, sometimes indeed douhie. While 

 every prepossession of the obsei'vei- was most sti-ietly avoided dnring 

 the measnrements, it was fonnd, that tiie centres of the dilfnse lines 

 really oscillate, tiie })eriod being 5,7333 days; Itiit, owing to the 

 nnsynimetricai appearance of many of the lines, no evidence could 

 be obtained that the valnes of the displacements were in mutual 

 agreement for all the lines on one and the same plate. Krom tiie 

 average displacements Hartmann calculated the "variable velocity in 

 the line of sight", and finally the elements of the oi-bit. 



An utterly surpi-ising result, yielded by the measiii-ements, was 

 that the calcinm line at X 3934, does not share in the 

 I)eriodic displacements of the other lines, but shows a 

 constant shift corresponding to a velocity in the line of sight of 

 -|- Hi km. (reduced to the Sun). 



Hartmann rejects the idea tiiat this line shoidd have originated in 

 the Earth's atmosphere; also the assumptioii tiiat it l)elongs to the 

 second component of the binary system. He is thus led to the hy- 

 pothesis that at some point in space ui the line of sight between 

 the Sun and (f Orionis there is a cloud of calcium vapour which 

 recedes with a velocity of It) k.m. \\\ examining the spectra of 

 neighbouring stars no further information as to the existence of such 

 a cloutl was obtaiiied. 



A cpiite similar phenomenon, lunvever, had been exhibited by the 

 spectrum of Nova Persei in 1901 : the lines of hydrogen and other 

 elements were enormously broadened and displaced and continually 

 changing theii- appearance, but during all the time the two calcium 

 lijies at Pv 3934 and P. 39(59, as Avell as the />-lines, wei-e observed as 

 perfectly sharj) absorption lines, yielding the constant velocity of 

 -|- 7 km. llART>rANN therefore assumes that also in the line of sight 

 between the Sun and Nova Hersei tiiere exists a nebulous mass 

 consisting, in this case, of calcium and sodium \a[>our, and moving 

 from the Sun at the i-ate of 7 km. a second. 



It nnist be adnnttcnl that these hy|)othetical clouds do not form 

 a satisfactory solution to the problem. 



