Review of Mrs. SomervUles Connexion of the Physical Sciences. 249 



Bat if it be shewn that the attraction of cohesion, by which materials are 

 held together, mechanically, and the attraction of affinity, by which sub- 

 stances are held together, chemically, be dependent for their power upon 

 the attraction of gravitation, and only modified in the application of it by 

 other causes, then would a real connexion, amounting indeed to an identity, 

 be shewn to exist between the sciences of Mechanics, Chemistry, and 

 Astronomy. Botany and Zoology are sciences subservient to Geology j 

 number and quantity are sciences connected with Astronomy. 



Before the connexion between the physical sciences can be displayed, it 

 is of course necessary to explain what those sciences are, and to what 

 extent they have been cultivated. By this exposition therefore the bulk of 

 the volume is occupied. 



The science with which the volume opens, is, of course. Astronomy. But 

 here the author has laboured under a difficulty, arising, perhaps necessarily, 

 out of the nature of the work. Astronomy is too important a science to be 

 disposed of satisfactorily in a few chapters ; and its higher conclusions are 

 too closely dependent upon its elementary steps, to admit of being fully 

 comprehended without them. Sir John Herschel's treatise was complete, 

 and therefore generally to be understood ; but Mrs. Somerville has been 

 obliged to confine herself to some of tlie higher parts of the science, 

 which do indeed display the connexions of this with other sciences, but 

 which require a previous acquaintance with the subject, more intimate than 

 falls to the lot of ordinary readers. 



But the astronomical sections of the work are nevertheless exceedingly 

 interesting, and the views unfolded in them vast and infinite. 



Tlius it is shewn to be analogically probable, whilst the satellites are 

 revolving round their primaries, these round the sun, and each is rotating 

 upon its own axis, that the sun, the centre of our system, is himself, with 

 all his revolving train, but a planet performing a wider revolution, 

 around a mightier sun than he. 



The section in which the perturbations, or variations, to which the sys- 

 tem is liable, are explained, is peculiarly striking. Of these, one class 

 depend upon the relative position of the orbs themselves, and being com- 

 pensated in periods comparatively brief, from a few months to less than a 

 thousand years, are called periodic variations ; while the other class, the 

 secular variations, depending not upon tlie position of the bodies them- 

 selves, but of the orbits in which they move, occupy periods of millions of 

 years, and affect not only the forms and planes of the several orbits, but 

 cause the great plane of the ecliptic itself to be in motion, and gradually to 

 recede from its original place. But the science, to which we owe the 

 knowledge of this tremendous fact, shews also that its extent is limited, 

 and that although the limits are unknown of that great cycle which will 

 extend into the immensity of time, yet that the very same cause to which 

 these secular inequalities are due, will itself necessarily bring about their 



