Dr. Playfair on the Nitroprusstdes. 271 



When over a place about 37 miles from the first-mentioned 

 place, its distance from the earth was 4)2 miles. 



When over a place about 80 miles from the first-mentioned 

 place, its distance from the earth was 25 miles. 



When over a place about 90 miles from the first-mentioned 

 place, its distance from the earth was 2S miles. 



When over a place about 1 1 miles from the first-mentioned 

 place, its distance from the earth was 19 miles, when it ex- 

 ploded. 



The curve described by the meteor was that of the para- 

 bola, as will be seen by laying the above numbers, or their 

 complements, to 84< miles, upon a line of abscissa. 



After the explosion, the luminous bodies were seen till they 

 were within 10 miles of the earth. The report accompanying 

 the explosion was so great, that I am inclined to believe that 

 the substance of the meteor was of a firm texture, broken 

 into many pieces by the extraordinary expansion of an elastic 

 fluid ; if so, its particles would fly off in all directions ; some 

 would describe parabolic curves, as mentioned by the Rev. 

 C. J. Goodhart ; some would continue to move with acce- 

 lerated force in the same direction, and some would fall ver- 

 tically. It seems probable that some parts of this body may 

 have reached the ground within a few miles round Biggles- 

 wade. It seems certain that this meteor must have come 

 from the regions of space far beyond the influence of our va- 

 pours ; and this fact, together with its extreme velocity, and 

 the intensity of the light, are circumstances more conformable 

 to a solid than to a gaseous substance. 



[The original accounts will be preserved in the Archives 

 of the Royal Observatory, Greenwich.] 



XXXIII. On the NitroprussideSt a New Class of Salts. 

 By Dr. Lyon Playfair, F.R.S., F.C.S. 



[Continued from p. 221.] 



Section III. — Changes experienced hy certain Nitroprusstdes 

 when their solutions are heated or kept. 



18. OEVERALofthenitroprussides, especially nitroprussic 

 1^ acid, nitroprussides of ammonium, barium and cal- 

 cium, deposit either prussian blue or oxide of iron when their 

 solutions are heated or are kept for some time. The residual 

 liquid, after evaporation, yields crystals of the same shape and 

 exactly of the same properties as before. Analysis however 



