410 



Septeinbor 20. 1904— expt sure Id-". 

 Iron and chromium comparison spectrum. 

 Abcuit 59 dark lines can bo counted between 

 (i and Ily. 



.'5. Specli-um of Venus, photographed 

 March 9. 1903. This is one of tl-.e set from 

 which I\Ir. Slipher determined the rotation 

 of the planet not to be of twenty-four 

 hours or thereabouts, but very Icng-— iron 

 comparison spectrum. 



4. Spectrum of ]\Iars, photographed 

 March 7, 1903 — iron comparison spectrum. 

 One of the plates of the set made on Mars 

 by ]\Ir. Slipher to test the measure of pre- 

 cision of the Venus set. The Mars plates 

 gave 25*^ 10™ ± for the planet's rotation. 

 The true value is 37i°. As the pre- 

 cision possible on Mars is only half that 

 possible for Venus the results speak for 

 the decisiveness of the Venus set. 



5. Spectrum of Jupiter, photographed 

 November 21, 1903— iron comparison spec- 

 trum. The tilt of the lines shows a rotation 

 in 9*^ 50"> ± , which is exactly the true rota- 

 tion period as determined by Spots. 



6. Spectrum of Saturn, ball and rings, 

 photographed September 7, 1904, on a 

 Cramer 'crown' plate— iron comparison 

 spectrum. The tilt of the lines of the ball 

 in one direction and that of the lines of the 

 rings in the other are well shown, demon- 

 strating that the rings are formed of dis- 

 crete particles, as proved mathematically 

 by Peirce in part and Clerk-IMaxwell in 

 whole and first shown spectrosccpically by 

 Keeler. 



The spectroscope used in these researches 

 was constructed by Brashear as powerful 

 as possible, especially for the determination 

 spectroscopically of the rotation period of 

 Venus. 



TJie CaiHih of Mars. An InvPs!irjalio)i of 

 Their Ohjcetiviiy: Percival Lowell. 

 A new and striking proof of the objectiv- 

 ity of the double canals of Mars has re- 



[X. S. Vol. XXL Xo. 53.3. 



cently come to me in a comparison of 

 the width of the doubles obtained by 

 Sohiaparelli in 1888 and by me in 1903. 

 The unintentional character of the cor- 

 roboration is one of its strongest points. 

 Not only at the time of my obsei*vatic.ns 

 was his work not in my mind, but not 

 even after the fact had I proposed to com- 

 pare it. 



The following table summarizes the re- 

 sults obtained in 1888 and in the May-June 

 presentation of 1903. 



CANALS DRAWN DOUBLE BY SCIIIAPAKELLI, 18S8. 



TinifSSeen. Width. 



o 



Euphrates 4 5.1 



Phison 4 3.9 



Astaboras 3 2.9 



Protonilus 4 2.2 



Pierus 4 2.4 



Canals drawn single by Schiaparelli : 

 Astusapes, Python, Xenius, Rhysius, Apis, 

 Typhon, Hiddekel, Callirrhoe,Deuteronilus. 



Two canals, Arnon and Kison, were 

 drawn convergent to the north. 



CANALS DRAWN 



DOUBLE BY LOWELL, 



1903. 





Times Seen. 



Width. 



Euphrates .... 



11 



o 



4.0 



Phison 



12 



3.7 



Astaboras .... 



9 



3.2 



Protonilus 



8 



2.8 



l^ierus 



•7 



2.1 



Sitaeus (faint) 



12 



3.6 



Canals drawn single by Lowell : Astu- 

 sapes, Python, Rhysius, Aroeris, Cadmus, 

 Jigyptus. Hiddekel generally single, Cal- 

 lirrhoe generally a broad line. 



Amon sometimes convergent to the 

 north, sometimes double. Kison suspicious 

 of convergence to the north. 



For both observers the direction of the 

 canal had nothing to do with its single or 

 double appearance. 



The conspicuous doubles are the same in 

 the drawings of both observers. 



SCIENCE. 



