292 PHILOSOPHICAL TRANSACTIONS. [aNNO 1728. 



and the like structure seems to be continued farther on into that sea itself. The 

 Pyrenean mountains also are only a continuation of that vast chain, which 

 begins in the Lepontiac Alpes, or the mountains in the Upper Vallesia, the can- 

 ton of Uri and Rhoetia, and from thence spreads itself chiefly west and south. 

 On the contrary, to the east and north they break off by degrees into gentle 

 plains, which appears evidently by the vast tracts of ground, which the Rhine 

 for instance, and the Danube compass, before they lose themselves, the one 

 into the German ocean, the other into the Black sea; whereas the Rhone, on 

 the other side, quickly, and with a proportionable velocity, reaches the Medi- 

 terranean. The same observation, with regard to the abrupt steepness of 

 mountains to the south and west, holds true in other parts of Europe, remark- 

 ably in England and Norway, more or less in other countries. And so far as 

 our maps and the accounts of travellers go, the same thing is observable in 

 other parts of the world, but most evidently in the high mountains of Peru 

 and Chili in South America, which terminate very abruptly westwards into the 

 Pacific sea, but gradually decline to the east into immense plains, watered by 

 some of the most considerable rivers in the known world, particularly the 

 river of Amazons and the Rio del la Plata, which arise in the said mountains. 



To conclude, from what has been hitherto said, it appears evidently, that the 

 mountains of Swisserland are the highest of Europe, and the great storehouse, 

 whence all the countries around them are supplied with water. 



Whether the depths of the sea correspond with the heights of mountains, 

 must be left to future observations. 



Optical Experiments made in the beginning of August 1728, before the President 

 and several Members of the Royal Society, and other Gentlemen of several 

 Nations; occasioned by Signior Rizzettfs Optics. By J. T. Desaguliers, 

 LL.D. and F. R. S. N" 406, p. 596. 



In 1727, Sig. Rizzetti, an Italian gentleman, published a book on the affec- 

 tions of light, in opposition to Sir Isaac Newton's doctrine, calling in question 

 several of Sir Isaac's experiments, because they did not succeed in the way he 

 tried them ; he also denies the consequence of others, and advances new hypo- 

 theses contrary to experience. 



The president of the Royal Society being acquainted with this, desired Dr. 

 Desaguliers to make some experiments on this occasion. How these were 

 made, and how they succeeded, with the inferences from them, are as follow: 

 first remarking, that some of these experiments are the same as Sir I. Newton's, 

 some also are his, but made in a different manner, and some are entirely the 

 Doctor's own. 



