PHYSICAL AND MATHEMATICAL SCIENCES. 1 17

dinary work, his “ Treatise on the Motions of thePlanet Mars.” He had devoted himself to this sub-ject at intervals from the commencement of his engage-ment with Tycho ; and the determined perseverancewith which he laboured at the most overwhelmingarithmetical calculations, is, perhaps, scarcely less sur-prising than the powerful genius which shines conspi-cuous in the successful treatment of so arduous anenquiry, or the wonderfully prolific imagination, whichwas never at a loss in starting a new theory to workupon when the last had been found insufficient. Thisvolume contains, in effect, the developement of two ofthose great laws of the planetary orbits by which thename of Kepler has been immortalised, and whichform the basis of the whole system of Newton. Theauthor seems thoroughly impressed with the import-ance of the work on which he is entering; and havingan eye to the prejudices which had been evinced withrespect to the promulgation of the Copernican system,and the views entertained by Tycho, he introduces hissubject in the following emphatic terms : —

“ If any one he too dull to comprehend the scienceof astronomy, or too feeble-minded to believe in Co-pernicus without prejudice to his piety, my advice tosuch an one is, that he should quit the astronomicalschools ; and condemning, if he has a mind, any or allthe theories of philosophers, let him look to his ownaffairs, and leaving this worldly travail, let him gohome and plough his fields ; and as often as he lifts upto this goodly heaven those eyes with which alone he isable to see, let him pour out his heart in praises andthanksgiving to God the Creator ; and let him not fearbut he is offering a worship not less acceptable than histo whom God has granted to see yet more clearly withthe eyes of his mind, and who both can and will praisehis God for what he has so discovered.”

In the introductory part of the work, the authordiscusses at length the received opinions respectinggravitation ; and after exposing many parts of the