Dean and Wohlei* on Tellurium and Selenium Compounds. 453 



metically speaking, both giving maximum values of the range; 

 the angle between them is 180— //•. 



Thus when h=Q, so that sin 6=0, /i4=90, and ^j — (^gi^ * 

 right angle, as may easily be verified. 



It may be worth while to exhibit the geometrical construction 

 for the case of firing from a gun in position commanding a hori- 

 zontal plane. 



Let A be the position of the 

 gun, LN a portion of a cii'cle 

 to radius AL which represents 

 the height of the gun above the 

 plain, LM twice the height due 

 to the velocity of projection, 

 ANM a semicircle on AM, P the 

 point in it bisecting thfe arc 



MN, then (abstraction made of the resistance of the air) AP is 

 the elevation at which the gun must be pointed to give the 

 greatest range on the plain below, for sec 2PAM obviously 

 _ . (velocity of ball)^ 



-^+ ^Tal • 



Suppose a sea battery as much as 300 feet above the water, 

 and a cannon-ball projected at the low rate of 1200 feet per 

 second (which is less than that of a common musket-ball), we 

 should have twice the height due to the velocity of projection 

 equal to 44720, and therefore 



44720 ^ 



^^'2^*= 1200+1 



= 88,2666, 



and consequently 2«=88° 30' 9" 



or «=44° 15' 5", 



differing very little from 45° ; showing that certainly in a non- 

 resisting medium, and in all probability in air, the height of the 

 point of fire above the plane which it commands will very little 

 indeed influence, under any conceivable circumstances of practice, 

 the angle of elevation which gives the best range. 



U, The Common, Woolwich, 

 April 30, 1856. 



LIX, Chemical Notices from Foreign Journals, 



By E. Atkinson, Ph.D. 



[Continued from p. 37B.] 



IN the January Number of Liebig's Annalen, Dean and Wohlcr 

 communicate the results of researches on tellurium and 

 selenium compounds. By acting on sulphamylate of potash by 



