478 PHILOSOPHICAL TRANSACTIONS. [aNNO 17Q5. 



the absolute resistance of the fiiiid in a direction perpendicular to the motion of 

 the planes. 



The law of resistance, when the velocity varies, may be thus found. Let iv 

 as before, be the sum of the 2 equal weights which will give the planes a uniform 

 horizontal motion when they move edgeways. Then set them perpendicular to 

 the horizon, and let w^ be the sum of the 2 equal weights, put one into each 

 scale, in order to give the sails the same uniform velocity. Take out these 2 equal 

 weights, and put in 2 other equal weights, together equal to a, such as shall give 

 the planes a uniform velocity double to that before given ; then the resistances 

 with these 2 velocities of 1 to 2 will be as w to q. If r be the sum of the 2 

 equal weights put into the scales to give a uniform velocity 3 times as great as 

 that of the first, then with velocities as 1 to 3 the resistances will be as w to r ; 

 and so on. This method was proposed by Mr. Robins, in order to determine 

 the law of resistance in terms of the velocity. If the planes be set at any angle, 

 we can by this means get, in terms of the velocity, the law of resistance not only 

 in the direction of the motion of the planes, but also in a direction perpendicular 

 to that of their motion. An account of all the experiments which can be made 

 by this machine, son)e of which I believe have never yet been attempted, I shall 

 lay before the r. s. at a future opportunity. 



JIf. On the Nature and Construction of the Sim and Fixed Stars. By IViUiain 

 Herschel, LL. D., F. R. S. p. 46. 



Among the celestial bodies the sun is certainly the first which should attract 

 our notice. It is a fountain of light that illuminates the world ! it is the cause 

 of that heat which maintains the productive power of nature, and makes the 

 earth a fit habitation for man! it is the central body of the planetary system ; and 

 what renders a knowledge of its nature still more interesting to us is, that the 

 numberless stars which compose the universe, appear, by the strictest analogy, to 

 be similar bodies. Their innate light is so intense, that it reaches the eye of the 

 observer from the remotest regions of space, and forcibly claims his notice. Now, 

 if we are convined that an inquiry into the nature and properties of the sun is 

 highly worthy of our notice, we may also with great satisfaction reflect on the 

 considerable progress that has already been made in our knowledge of this eminent 

 body. It would require a long detail to enumerate all the various discoveries 

 which have been made on this subject ; I shall therefore content myself with 

 giving only the most remarkable of them. 



Sir Isaac Newton has shown that the sun, by its attractive power, retains the 

 planets of cur system in their orbits. He has also pointed out the method by 

 which the quantity of matter it contains may be accurately determined. Dr. 



