294 



SCIENCE. 



[N. S. Vol. XV. No. 373. 



of the condensations were seen to have 

 moved appreciably, while the strong one 

 nearest the Nova showed but little if any 

 change. An exposure of ten hours was se- 

 cured on the nights of December 8 and 11, 

 the 9th and 10th being cloudy. The motion 

 of the nebula is so rapid that even in this 

 interval of three days, blurring in the best- 

 marked condensation is noticeable. A com- 

 parison of the last negative with that of 

 November 12 and 13 reveals a number of 

 changes. Condensations A, B and C 

 (Lick Observatory Bulletin No. 10) have 

 each continued their motions to the south- 

 east full I'. Condensation D shows little 

 or no change. Perhaps it is moving nearly 

 in the line of sight. The negatives of De- 

 cember 4 and 8-11 show two new wisps of 

 nebulosity southwest of. the Nova at dis- 

 tances of 13' and 14', respectively. They 

 are approximately arcs of circles of which 

 Nova is the center and are about 2' in 

 length. They have been carefully looked 

 for on the November negatives, but no 

 traces are there found of them. Through- 

 out the entire southeast quadrant faint 

 nebulosity is shown to a distance of 18' on 

 the negative of December 8-11. There 

 is but little appearance of structure in this 

 outlying nebulosity. Several wisps of 

 nebulosity 6' to the north of Nova are suffi- 

 ciently strong to show that motions out- 

 ward of i' to I' have taken place in the 

 interval of 27 days. A wisp 9' to the north 

 has also moved outward full ^'. 6' to the 

 northwest of Nova is a wisp which has 

 moved outward i'. None of these wisps to 

 the north and northwest are well enough 

 defined lengthwise to make the other com- 

 ponent of motion certain in the interval. 

 Directly to the west is an arrow-shaped 

 mass of nebulosity resembling somewhat 

 the structure of condensation A. It has 

 certainly moved outward and there appears 

 to have been a motion to the northwest. 

 Many changes of form and intensity of 



masses of nebulosity have been noticed 

 other than those referred to above, but 

 which can not well be described. A longer 

 series of photographs is necessary to deduce 

 the character and amount of motion of 

 these fainter masses. Lantern slides of 

 the various photographs secured with the 

 Crossley reflector were exhibited. 



A Determination of the Wave Lengths of 

 the Brighter Nebular Lines: W. H. 

 Wright. 



In the progress of our investigations 

 upon the spectrum of Nova Persei (see 

 Lick Observatory Bulletin No. 8) there 

 arose the necessity for a more accurate 

 knowledge than then existed of the wave 

 lengths of the Brighter Nebular lines. The 

 spectra of the Orion Nebula and of three 

 of the brighter planetary nebula have been 

 photographed in some eases with one prism, 

 and in other cases with three prisms, and 

 the resulting plates have been measured 

 and reduced. The wave lengths of 16 

 bright lines have been determined with con- 

 siderable accuracy, the fifth significant 

 figure being determined definitely for the 

 principal ones, and the uncertainty in the 

 sixth place for the brighter lines being 

 comparatively small. A slight correction 

 appears to be needed in the values at pres- 

 ent accepted for the positions of the two 

 chief nebular lines determined by visual 

 means. In the course of the work three 

 new nebular lines have been discovered. 

 The well-known lines usually described as 

 He and X 3,727 have been found to be 

 double. 



A Determination of the Cause of the Dis- 

 crepancy betiveen Measures of Spectro- 

 grams made luith Violet to Left and with 

 Violet to Bight: H. M. Eeese. 

 In this paper three possible causes of 

 the effect in question are investigated: (1) 

 The curvature of the spectral lines; (2) 

 the position of the star-spectrum in the 



