1909] 



on Recent Results of Astronomical Research. 



575 



Envelopes of Comet C 1908. Oct. 27. 

 (Distance of the vertex of the envelope from the nucleus of the comet.) 



(1) Deduced from measurements made at the vertex. 



(2) Deduced from measurements of the course of the envelope near the 

 ends of the latus rectum. 



of envelopes ; it indicates that the explosion is strongest at first, and 

 then dies down rapidly. But we can make another deduction : the en- 

 velope was beginning to form at 8 h. 23 m. ; by 9 h. P> m. the complete 

 arch was visible. Now it can be shown theoretically that the formation 

 of an envelope does not take place instantaneously along the entire arch ; 

 if, for example, the material forming the apex left the nucleus an hour 

 previously, that forming the ends of the latus rectum left an hour and 

 twenty-five minutes previously, and so on in proportion. Conversely, 

 we can argue from the fact that the whole arch appeared in so short 

 a time, and that the ends of the latus rectum begin to collapse very 

 little, if at all, after the apex, that the time taken by the matter to 

 travel from the nucleus to the apex must be very small. I dare not 

 trust the figures in the Table so far as to calculate that time from them, 

 but probably it will be a very safe outside limit if we say that that time 

 is not more than two hours. A simple calculation shows that, for 

 that to be the case, the solar repulsion acting on these particles must 

 be at least 800 units— far larger than any repulsion calculated by 

 Bredichiu, Jaegermann, or others ; the velocity of projection would 

 need to be 70,000 miles per hour. These figures are far too startling 

 for us to immediately accept them, though, of course, if it is 

 admitted that the repulsion acts only for a short time, instead of 

 continuously, it must be correspondingly more powerful during that 

 time. We are at the beginning not at the end of an investigation ; 

 but I am convinced that a greal deal is to be learnt from the study 

 of these envelopes. Unfortunately they are often very complicated. 

 Sometimes two of them will intersect, or they may be all askew. That 

 need not be considered surprising, for the simple parabolical form can 

 only occur when the force of the explosion is equal in all directions. 



Another feature sometimes possessing some degree of regularity 

 is the waving of the streamers proceeding from the head. This is a 

 feature which will certainly repay a much more careful examination 

 than we have yet had time to give. The most immediately striking 



