100 Mr. Shelford Bidwell [May 5, 



colour, which has sometimes been likened to that of pease soup : their 

 density is abnormal, so is their persistence ; and they often occur 

 when the temperature of the air is considerably above the dew point. 

 But what renders them especially objectionable is their acrid and 

 corrosive quality, in virtue of which they exert a highly deleterious 

 action upon animal and vegetable life. 



The uncleanness of a town fog is of course due to the sooty and 

 tarry matters with which it is charged, and which are derived from 

 the smoke of innumerable fires. Its other and more mischievous 

 specialities are mainly attributable to certain products of the com- 

 bustion of sulphur, a substance which exists in relatively large 

 proportions (from half to one per cent.) in nearly all varieties of 

 coal. 



We may make a sample of London fog in the glass globe by 

 burning a little sulphur near the orifice of the inlet pipe while air is 

 being admitted; and in order to prevent the entrance of any solid 

 particles of sublimed sulphur, we will filter the air through a little 

 cotton wool. The fog formed when the air is expanded far exceeds 

 in density any we have yet seen. The globe appears almost as if it 

 were filled with something that could be cut with a knife. 



This is hardly the time or the place to discuss the possible 

 methods by which town fogs might be abolished as such, or rendered 

 as innocuous as those of the country. It is impossible to doubt that 

 year by year they are increasing in virulence, and when the burden 

 of the evil becomes too grievous to be borne, as is likely to be the 

 case before many more winters are past, the remedy will perhaps be 

 found in the compulsory substitution of gas for coal as the ordinary 

 domestic fuel. 



Every one has noticed how dense and dark a thundercloud is. It 

 shuts out daylight almost as if it were a solid substance, and the 

 glimmer that penetrates it is often imbued with a lurid or copper- 

 coloured tint. 



I had always found it rather difficult to believe that these 

 peculiarities were due simply to the unusual extent and thickness of 

 the clouds, as is commonly supposed to be the case, and it occurred 

 to me about three years ago, that perhaps some clue to the explana- 

 tion might be afforded by the electrification of a jet of steam. On 

 making the experiment I found that the density and opacity of the 

 jet were greatly increased when an electrical discharge was directed 

 upon it, while its shadow, if cast upon a white screen by a sufficiently 

 strong light, was of a decidedly reddish-brown tint. 



As a possible explanation of the effect I suggested that there 

 might occur some action among the little particles of water of a 

 similar nature to that observed by Lord Eayleigh in his experiments 

 upon water jets. Perhaps you will allow me to show his fundamental 

 experiment before further discussing the steam jet. 



A jet of water two or three feet long is made to issue in a nearly 

 vertical direction from a small nozzle. At a certain distance above 



