156 On Bright Lines in the Spectra of Star Clusters. [Apr. 19, 



repeat themselves. This would explain why the action of spongy iron 

 continues so long. 



It is, however, quite certain that there is also a reducing action taking 

 place when ordinary water is passed through spongy iron. This is clearly 

 indicated by the reduction of nitrates. 



Our knowledge of those low organisms which are believed to be the 

 cause of certain epidemics is as yet too limited to allow of direct experi- 

 ments upon them. It is not improbable that, like the Bacteria of putre- 

 faction, they are rendered harmless when water containing them passes 

 through spongy iron ; but until we possess the means of isolating these 

 organisms, this question can only be definitively settled by practical 

 experience. Should this not be satisfactory, should those specific con- 

 tagia not be destroyed when passing in water through spongy iron, then 

 the separation of Bacteria by spongy iron may afford means of isolating 

 those germs of disease ; should it be favourable, then we shall have found 

 in spongy iron the material to prevent the spreading of epidemics by 

 potable water. 



II. " On a Cause for the Appearance of Bright Lines in the 

 Spectra of Irresolvable Star Clusters." By E. J. Stone, 

 M.A., E.R.S., Her Majesty's Astronomer, Cape of Good 

 Hope. Received March 20, 1877. 



Before the announcement of Mr. Huggins's discovery of the presence 

 of bright lines in the spectra of nebulae, it was generally, if not univer- 

 sally, accepted as a fact that nebulas were merely stellar clusters irresol- 

 vable on account of their great distances from us. This view had become 

 impressed on the minds of many of our greatest observing astronomers 

 in the progress of their work, and is one therefore which should not 

 lightly be abandoned. 



It appears to me that Mr. Huggins's observations, instead of being 

 inconsistent with the view formerly held by astronomers, are rather con- 

 firmatory of the correctness of that view. 



The sun is known to be surrounded by a gaseous envelope of very con- 

 siderable extent. Similar envelopes must surround the stars generally. 

 Conceive a close stellar cluster. Each star, if isolated, would be sur- 

 rounded by its own gaseous envelope. These gaseous envelopes might, 

 in the case of a cluster, form over the whole, or a part of the cluster, a 

 continuous mass of gas. So long as such a cluster was within a certain 

 distance from us, the light from the stellar masses would predominate over 

 that of the gaseous envelopes. The spectrum would therefore be an 

 ordinary stellar spectrum. Suppose such a cluster to be removed further 

 and further from us. The light from each star would be diminished in 

 the proportion of the inverse square of the distance ; but such would not 



