60 



SCIENCE. 



[N. S. Vol. V. No. 106. 



Polytechnic Institute of Graz, has been pro- 

 moted to an assistant professorship of Geom- 

 etry and Dr. W. Felix, of the University of Zu- 

 rich, to an assistant professorship of anatomy. 



n\, 



DISCUSSION AND CORRESPONDENCE. 



CLOUDS OVEE A FIRE. 



On Tuesday, December 1st, I had an excel- 

 lent opportunity to observe the formation of 

 cumulus clouds over the smoke from a large 

 fire. The morning was clear, with the excep- 

 tion of a few scattered strato- cumulus and 

 cumulus clouds near the horizon. The wind 

 was northwest and blowing at about 12-15 

 miles an hour. The Are was in the coal pockets 

 of the Boston and Maine Railroad, in Charles- 

 town, and burned fiercely for some hours, send- 

 ing up immense volumes of smoke which were 

 blown off to sea across the city of Boston. The 

 cloud, as I observed it, looking from the south- 

 west and thus obtaining a view at right angles 

 to the smoke, was formed at some little distance 

 to the southeast of the fire, and over a part of 

 the smoke, which rose up higher than the rest, 

 as is shown in Fig. 1. It was distinctly a 

 cumulus, but its base and a good deal of its 

 main portion were often obscured by the smoke. 

 Fig. 2 is intended to give some idea of what was 

 observed as the second stage in the phenom- 

 enon. The whole body of the cloud has been 

 carried to the southeast, further away from the 

 fire, and the effect of the stronger upper winds 

 is seen in the blowing forward of the top of the 

 cloud. At this stage the cloud could plainly be 

 seen to be dissolving as it descended to lower 

 levels. 



In Fig. 3 we have represented, to the right, 

 the third stage of the cloud, which is now rap- 

 idly diminishing in size and being carried away 

 by the wind, while nearer the fire a new cumu- 

 lus has been formed. It was noted that the 

 formation of the cumulus in its first position, as 

 shown in Fig. 1 and at the left of Fig. 3, was in- 

 termittent. There was not always a cloud at 

 that point, but one grew whenever there was 

 an especially active ascent of the smoke, and 

 the position of this first cloud, at its beginning, 

 was always the same with reference to the fire 

 and the trail of smoke. 





-r_iiL 



%«(■ 



There seems little need of comment on this 

 simple but interesting phenomenon. The con- 

 ditions for cloud formation were not reached 

 vertically over the fire, for the smoke was 

 blown to leeward at once, and the warmed air 

 did not rise high enough to reach its dew-point 

 until it had been blown a-quarter or a-half of a 

 mile to the southeast. For this reason Figs. 1, 

 2 and 3 show the cloud to the right of the fire. 

 Looked at down the wind, i. e., from the north- 

 west, the appearance of smoke and cloud were 

 as shown in Fig. 4. 



It may be interesting to note in this connec- 

 tion the case of cloud formation over a fire 

 mentioned by Espy in his Fourth Meteorological 

 Report. The observer quoted by Espy was on 

 the top of Mt. Monadnock, N. H., and saw the 

 growth of a cumulus cloud over a fire of brush 

 on the lowland. The cloud increased in size, 

 and finally gave a shower of rain over a limited 

 area. 



The accompanying figures were drawn by 



