TRANSACTIONS OF THE SECTIONS. 35 



that under ordinary conditions of the spark, when the characteristic lines of lead 

 are strong, this line is seen only in the part of the metal vapour which is close to 

 the electrode. I found, however, that under other conditions of the electric dis- 

 charge this line extends across the spectrum, and becomes bright, at the same time 

 that the principal lines of the lead-spectrum are very faint. 



A simultaneous comparison of this line with the brightest of the lines of the 

 nebulffi showed that, if not truly coincident, it was sufficiently so, under the powers 

 of dispersion which can be applied to the nebulas, to serve as a fiducial line of com- 

 parison in the observations which I had in view. 



I need not say that the coincidence of the lines does not indicate the presence 

 of lead in the nebula. 



I found that in the spectrum of the great nebula in Orion, at the same time that 

 the third line was seen to be coincident with H;8, the first line appeared to coincide 

 with the line in the spectrum of lead. There was a very slight apparent excess of 

 breadth in the nebular line, due possibly to its being in a small degree the brighter 

 of the two, which appeared to extend towards the red, so that the more refrangible 

 sides of the lines were in a right line. 



The lead line could now be used as a fiducial line for the examination of the 

 motion of the nebulae which are too faint to permit of direct comparison with hy- 

 drogen. 



By this method the following nebulae have been carefully examined. In all 

 these nebulae the relative position of the first nebular line with the lead line was 

 found to be exactly the same in a spectroscope containing two compound prisms 

 which together give a dispersion about equal to that of four single prisms of dense 

 flint of 60°. 



The results, though negative, are, however, not without interest, as they show 

 that these nebulae were not moving toward or from the earth with a velocity so 

 great as thirty miles per second. 



List of Nebulae . 



h. H. 



No. 1179, 360. M. 42. 



No. 4234. 1970. 2. 5. 



No. 4373. IV. 37. 



No. 4390. 2000. 2. 6. 



No. 4447. 2073. M. 57. 



No. 4510. 2047. IV. 51. 



No. 4964. 2241. IV. 18. 



The numbers in the above list are from Sir J. Herschel's ' General Catalogue of 

 Nebulae.' 



On the Application of Photography to show the passage of Venus across the 

 Sun's Disk. By M, Janssen. 



Results of some recent Solar Investigations. By J. Norman Lockyee, F.R.S. 



On the Visibility of the DarJc side of the Planet Venus. 

 By Professor A. Schafabik, Prague. 



[Ordered to be printed in extenso among the Reports.] 



