PEOGEESS m ASTEONOMY. 125 



With the then existing- methods of computation of orbits it was 

 imperative to have numerous measured positions to use as data for the 

 calculation. The scant}^ data available in the case of Ceres were not 

 sufficient for the application of the method. The occasion discovered 

 a man, one of the greatest mathematicians of the nineteenth century, 

 Karl Frederick Gauss, who, although only '25 A^ears of age, undertook 

 the solution of the problem by employing a system which he had 

 devised, known as ""the method of least squares," w^hich enabled him 

 to obtain a most probable result from a given set of observations. 



This, with a more general method of orbit computation, also elabo- 

 rated b}^ himself, was sufficient to enal)le him to calculate future posi- 

 tions of Ceres, and on the anniversary of the original discovery, Olbers, 

 another great pioneer in orbit calculations, found the planet in very 

 nearly the position assigned by Gauss. So great was the curiosity 

 regarding the other portions of the planet, which was supposed to have 

 been shattered, that numerous observers at once commenced to search 

 after other fragments. 



These were the actualities of 1801 and thereabouts, but the seed of 

 much future work was sown. Kant and Laplace had already occupied 

 themselves with theories as to the world formation, and spectrum anal- 

 ysis as applied to the heavenly bodies may be said to have been started 

 by WoUaston's observations of dark lines in the solar spectrum in 1802. 

 Fraunhofer was then a boy at school. In the same year the first pho- 

 tographic prints were produced by Wedgewood and Davj^. 



OBSERVATORIES. 



It has been stated that at the beginning of the century there were 

 no permanent observatories, either in the southern hemisphere or in 

 the United States. The end of the century finds us with two hundred 

 observatories all told, of which fourteen are south of the equator and 

 forty-seven in the United States, among which latter are the best 

 equipped and most active in the world. 



The observatory of Parramatta was the first established (in 1821) in 

 the Southern hemisphere. This was followed by that of the Cape of 

 Good Hope in 1829. Of the more modern southern observatories from 

 which the best work has come we may mention Cordova, the seat of 

 Gould's important investigations, established in 1868, and Arequipa, a 

 dependency of Harvard, whence the spectra of the southern stars have 

 been secured, erected still more recently (1881). 



I believe, but I do not know, that the large number of American 

 observatories have radiated from Cincinnati, where^ in consequence of 

 eloquent appeals, both by voice and pen, from Mitchell, then professor 

 of astronomy, an observatory was commenced in 1815. There can be 

 no doubt that at the present moment, with the numerous well-equipped 



