ASTRONOMICAL AND PHYSICAL OBSERVATORIES. 367 



marquable qu'un Astronome, sans sortir de son observatoire, en com- 

 parant seulement ses observations a Panalyse, cut pu determiner ex- 

 actement la grandeur et l'aplatissernent de la terre, et sa distance au 

 soleil et a la lune, elernens dont la connaissance a ete le fruit de longs 

 et sensibles voyages dans les deux hemispheres," x etc. (6me edition, 

 p. 232). 



It is evidently not the purpose of Theoretical Astronomy, then, to 

 train faculties other than those employed in the higher mathematical 

 investigations, and for this purpose no observatory is strictly neces- 

 sary. But Physical Astronomy, as usually taught, confines itself to 

 Descriptive Astronomy, and for that study it is undoubtedly necessary 

 that students should have access (and a far freer access than they 

 usually have) to instruments. To supply this want, " instruments of 

 the largest size " have been too frequently supplied, so that it is pos- 

 sible that the student may contemplate the features of the moon, or 

 the components of a coarse double star, through a 15-inch, nay, per- 

 haps, a 20-inch object-glass, when perhaps a 4-inch telescope of 

 Alvan Clark's make would serve the student's and the college's pur- 

 poses fully. It used to be a saying of a celebrated American astrono- 

 mer that " the price of telescopes increased directly as the cubes of the 

 diameters of their object-glasses." If no higher ratio be the true one, 

 it is evident that in the case supposed we have force misapplied, or not 

 applied at all. It has become almost a reproach for a college not to 

 own an equatorial of at least eight inches clear aperture ; yet only con- 

 sider how much of the best work of astronomy has been done with 

 less apertures ! Sir John Herschel and Sir James South executed a 

 long and very refined series of measures of double stars with a much 

 smaller instrument than the ordinary college equatorial, and much of 

 Struve's best work is recorded as done with "the smaller instru- 

 ments," and so on. It is not intended to advocate the use of poor in- 

 struments, nor specially of small ones, but to point out that the means 

 should be adjusted to the object in view, and that no waste of power 

 should be permitted. Again, Spherical Astronomy is taught in some 

 colleges ; and, in considering this branch of the subject, we are touch- 

 ing on its most useful portion. In nothing is a student's habit of 

 accuracy more trained than in astronomical observation. There are 

 minor points to be attended to each moment, and it is not until he 

 ceases to be a pupil that he begins to be thoroughly at ease with even 

 the simplest instrument. He has a running commentary of reasoning 

 to make constantly, which is of the greatest value to him. He must 

 constantly ask himself, while using his instruments, " If I do this or that, 

 what will happen, and why ? " Now, it is presumably to forward this 



1 It is a very noteworthy fact that an astronomer, without quitting his observatory, 

 but by merely submitting his observations to analysis, could have determined exactly 

 the dimensions of the earth, its oblate form, and its distance from sun and moon data 

 which have been obtained as the fruit of long and arduous voyages in both hemispheres. 



