VOL. VI.] PHILOSOinirCAL TRANSACTIONS. 5/5 



III. Physico Mathcsis dc Lumiiic, Coloribus et Iridc, &c. Auth. Franc. 

 Maria Grimaldo,* J. S. Bononiac, 1605, in 4to. 



The author finding that much obscurity was left in the doctrine of light, and 

 esteeming it rather commendable than presumptuous to endeavour the clearing 

 of it, especially if that be done by experiments (which he accounts an excellent 

 way for the improvement of all natural knowledge) undertakes in two parts to 

 deliver his trials and meditations on this subject. 



In the first are contained the several experiments which may favour the doc- 

 trine of the substantiality of light, together with the ratiocinations thence 

 arising. In the second is represented what may be answered to all those argu- 

 ments, so as to save the peripatetic opinion of the accidentality of light. 



But more particularly, in the former part, he explains how many ways light is 

 propagated or diffused, viz. not only directly, and by refraction and reflection, 

 but also by diffraction, which last, according to him, is done when the parts of 

 light, separated by a manifold dissection, do in the same medium proceed in 

 different ways. Next he considers the nature of light, as also diaphaneity and 

 opacity, and takes notice that most bodies, whether solid or fluid, are porous; 

 on which occasion he ventures to explain almost the whole philosophy of mag- 

 netics. Then he discusses the question, whether the diffusion of light be in- 

 stantaneous, and concludes it in the negative, though the duration of it be im- 

 perceptible. This done, he examines the nature of reflection and refraction, 

 and seems to acknowledge, that supposing light to be a substance very fluid and 



* Father Grimaldi was one of those philosophers of the I7th century to whom the sciences of as- 

 tronomy and optics lie under great obligations. Those sciences he cultivated in compact with his 

 compatriot Riccioli, by diligent observations and experiments. He first noticed the spots in tlie sun, 

 and gave to those in the moon names that are still in use^ denominating them after the most eminent 

 astronomers and philosophers. He made numerous experiments in optics, and some discoveries, 

 which were afterwards confirmed and much farther extended by the brilliant discoveries of Newton. 

 Grimaldi discovered tlie circumstance of the lengthening of the solar image, by a ray of light let in 

 through a small hole, and refracted through a glass prism, but without, however, discovering tlie dif- 

 ferent refrangibility of the rays. He taught also tliat the rays are of different colours, and that opaque 

 objects have no colour but what tliey receive firom the rays of light. He discovered that property of 

 the rays by which, when they pass near the edge of certain objects, though witliout touching, they 

 are inflected or bent from their direct course, an effect which he termed the diffraction of light, and 

 which Newton afterwards called the inflection of it. Indeed the above work of Grimaldi comprises 

 a great quantity of curious experiments and remarks on light and colours. This indeed was his chief 

 merit J for his philosophy is but too much after the manner of his country, which although it has gi- 

 ven to the world a Galileo, a Torricelli, &c. was not tlie first to shake off the yoke of Aristotle. It 

 must, however, be acknowledged to the honour of Grimaldi, that had he lived in another countr}', and 

 under another authority tlian that of his society, he would have boldly opposed the dogmas of the an- 

 cient philosophy. Add to this, that he was cut off at a very early period, viz. in 1663, at only 44 

 years of age. 



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