330 SPECIAL RESULTS IN THE URANOLOGICAL 



direction." The obliquity of the ecliptic was regarded as a 

 cosmical event, an alteration which took place suddenly no 

 allusion was made to a subsequent progressive change* 



The description of the two extreme or opposite cases, to 

 which the planets Uranus and Jupiter approximate most 

 nearly, is suited to remind us of the alterations which the 

 increasing or decreasing obliquity of the ecliptic would pro- 

 duce in the meteorological relations of our planet, and in the 

 development of organic forms, if this increase and decrease 

 were not restricted within very narrow limits. The recog- 

 nition of these limits has been the object of the great 

 labours of Leonhard Euler, Lagrange, and Laplace, and 

 may be regarded as one of the most brilliant achievements 

 of theoretical astronomy in modern times, and of the degree 

 of perfection to which the higher analysis has been brought. 

 The limits in question are indeed so narrow, that Laplace, 

 in the Exposition du Systeme du Monde, ed. 1824, p. 303, 

 stated that the obliquity of the ecliptic only oscillates 1 J on 

 either side of its mean position. This is equivalent to saying that 

 the torrid zone, or the tropic of Cancer, which is its northern 

 boundary, can only approach by that quantity nearer to the 

 part of the Earth in which we live ( 53 ), or that, leaving out 

 of view the effects of the many other causes of meteorological 

 perturbations, Berlin might be gradually transferred from its 

 present isothermal line to that of Prague. The implied ele- 

 vation of the mean annual temperature would hardly be 

 more than one degree of the centigrade thermometer (1*8 

 Fah.) ( 531 ). Biot, though also believing the variations of 

 the obliquity of the ecliptic to be restricted within narrow 

 limits, yet deems it more advisable not to attempt at present 

 to assign to them definite numerical values. He says "La 



