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form of a hollow cone, which would account for the 

 frequently observed apparent division of the tail into two 

 lateral branches, for this hollow envelope being oblique to 

 the line of sight at its borders a greater depth of illuminated 

 matter would there be exposed to the eye. 



As the comet proceeds along its path it will project a 

 newer shadow at an angle from that which it has already 

 cast, the mist formed in which latter will be dispelled by 

 the unimpeded action of the solar rays, whilst another 

 portion of the comet's atmosphere will suffer partial con- 

 densation, thus causing the formation of a new tail and the 

 dissipation of the old one to take place simultaneously, and 

 accounting for the enormous sweep which the tail makes 

 round the sun in perihelio in the manner of a rigid rod, and 

 in seeming defiance of gravitation and all mechanical law. 



The extent to which condensation in the cometary atmos- 

 phere will take place will obviously depend, amongst other 

 things, on the difference of temperature within and without 

 the shadow, and on the length of time during which that 

 difference of temperature is allowed to operate. Now the 

 further from the nucleus we go the fainter and the more 

 diffuse the shadow will become; and apart from this, as 

 well as in consequence thereof, the less the difference of 

 temperature within and without that shade, and the longer 

 the time required to effect a condensation. Accordingly 

 the axis of the conoidal envelope will lag behind the axis 

 of the shadow, the more so as we recede from the nucleus, 

 thus producing the observed convexity on the tail's orbital 

 preceding side. 



The further we are from the nucleus, however, and for the 

 same reason, the longer will be the time required to evapo- 



