J^etv Mineralogical Hamnur. 715, 



sec. and the last acquired velocity being double of the mean 

 velocity is, in this case, 8 feet per second. But the spa- 

 ces described are always as the squares of the last acquired 

 inch. sqr. ofvel. inch. sq. ofvel. 



velocities. Hence, 12 : 8X8 = 64 : : 5^ : 28. 

 Hence \/2B=5.29 feet per second, or upwards of 3i miles 

 per hour, is the velocity acquired in falling 5{ inches, in- 

 stead of ]| feet per second, and l^\ miles per hour, as es- 

 timated by your correspondent. B. F. J. 

 June, 1823. 



4. JVeuj Mineralogical Hammer, by Rev. E. Hitchcock, A.M. 



"I have lately constructed a geological hammer* on such 

 a plan as to embrace three or four of those used in Europe, 

 both for convenience and economy. Fig. 1 is a side view 

 of the hammer. The lower part a of the head a 6, is a 

 little rounded to endure a heavier blow. Yet this curva- 

 ture ought not to be very great, as a flat surface is often ad- 

 vantageous. The upper pan b, of the head, is brought to 

 an edge : the direction of the edge coinciding with that of 

 the handle, as shown in Fig. 2. In the handle, a hole six 

 or eight inches deep, and half or three quarters of an inch 

 in diameter, is made to receive a steel drill, e f. This, 

 when not wanted, is confined in the handle by a spring rf, 

 closing down so as to cover the hole at e. The hammer 

 without the handle, weighs about two pounds. The handle 

 should be made rather larger than is common, as it is liable 

 to split when heavy blows are struck while the drill is in- 

 serted in it. 



The rounded face of the hammer a is used in breaking 

 specimens from the obtusely angular surfaces of rocks ; the 

 edge b serves to cleave schistose or laminated specimens, 

 and to break common specimens in the cabinet, and the 

 drill is often wanted to assist in disengaging petrifactions or 

 minerals deeply imbedded in their matrix." 



5. Navigation of Rapids. 



Mr. Edward Clark has recently published in Philadel- 

 phia, a " Description of a plan for navigatmg the rapids m 



* See Plate 5. 



