1862.] 327 



dry air being caused to displace moist, and moist air dry, in the open 

 atmosphere. He considers and removes objections, and points out 

 the bearing of his experiments on various questions in meteorology. 

 The formation of cumuli and the cause of the tropical rains are con- 

 sidered ; the effect which the absence of aqueous vapour must have 

 upon climate is pointed out ; and the a priori conclusions to be drawn 

 from the experiments are shown to agree with observation. Reference 

 is made to anomalies of observation which have been hitherto unex- 

 plained, but which admit of easy solution by reference to the radiant 

 arid absorbent power of aqueous vapour. The author endeavours to 

 supplement the views hitherto entertained regarding the action of 

 mountain masses as condensers of the atmospheric moisture. He 

 accounts for the enormous radiation observed at great elevations, and 

 concludes by showing the possible bearing of his results on the theory 

 of " Serene" and of hail. 



III. "Distribution of the Surface of the Third Order into 

 Species, in reference to the absence or presence of Singular 

 Points, and the reality of its Lines." By Dr. SCHLAFFLE, 

 Professor of Mathematics in the University of Berne. 

 Communicated by ARTHUR CAYLEY, Esq. Received 

 December 18, 1862. 



(Abstract.) 



The theory of the 27 lines on a surface of the third order is due 

 to Mr. Cayley and Dr. Salmon ; and the effect as regards the 27 lines 

 of a singular point or points on the surface, was first considered 

 by Dr. Salmon in the paper " On the triple tangent planes of a surface 

 of the third order," Camb. and Dub. Math. Journ. t. iv. pp. 252- 

 260 (1849). The theory as regards the reality or non-reality of the 

 lines on a general surface of the thirdorder,is discussed in Dr. Schlaffle's 

 paper, "An attempt to determine the 27 lines, &c.," Quart. Math. 

 Journ. t. ii. pp. 56-65, and 110-120. This theory is reproduced 

 and developed in the present memoir under the heading, I. General 

 cubic surface of the third order and twelfth class ; but the larger 

 part of the memoir relates to the singular forms which are here first 

 completely enunciated, and are considered under the headings II., 



