VOL. XXX.] PHILOSOPHICAL TRANSACTIONS. 405 



sowed but ,41^0 0^ ^^ ounce, was increased in weight according to the follow- 

 ing proportions, viz. 



In 6 weeks time 67 1,600 ") 



!week 11] ,933-i- / 

 day 1 5,990^ > times its own weight, 

 hour 666i I 

 minute of an hour 1 1 J 



Some time after, another ounce of the same sort of seed was exactly weighed, 

 and the grains were found to be in number 14673. 



Another turnip of the same crop was taken upon the 21st of October, 

 which weighed above lO-l lb.; which unusual and truly wonderful bulk it ac- 

 quired by increasing the weight of the seed it was raised from, 15 times in 

 every minute of an hour, from the sowing to the drawing it. Besides, the 

 gardener neglected to thin his turnips in due time, otherwise probably their 

 growth had been more considerable. 



At another time in two other sorts of turnip-seed, it was found by counting 

 that 1 oz. of one sort contained 14/02 grains; and 1 oz. of the other sort 

 14905 grains. 



It is credibly reported, that of late years turnips have been pretty frequently 

 found growing in several counties of this kingdom that have weighed above 

 twice as much; one of which was seen at Birmingham about the year 1710. 



An Account of Experiments made ivith Mons. Fillette's Burning Concave^ in 

 June 17 18. By the Rev. Dr. J. Harris, F.R.S, and Dr. J. T, Desaguliers, 

 RR.S. N°36o, p. 976. 



This mirror is a concave, 47 inches wide, and ground to a sphere of 76 

 inches radius ; so that its focus is about 38 inches distant from the vertex of the 

 glass. The metal, of which it is made, is a mixture of copper, tin, and tin- 

 glass, and it§ reflection has something of a yellow cast. The concave surface 

 has scarcely any flaws, and those very small ; but the convex side, which is also 

 polished, has some holes in it. 



Having held several bodies in the focus of this mirror, we observed what 

 happened to them while exposed to this great heat; and with a half second 

 pendulum noted the time in which any material change happened to them. The 

 experiments were made from 9 till 12 in the morning, as follow: 



N° 1. A red piece of a Roman patera, which began to melt in 3 seconds, was 

 ready to drop in 100. — 2. Another black piece melted at 4, and was ready to 

 drop in 64 seconds. — 3. Chalk taken out of an echinus spatagus filled with 

 chalk only, fled away in 23 seconds.— S^. A fossil shell calcined in 7 seconds, 



