PROGRESS OF METEOROLOGY IN 188<J. 257 



At the Americau Associatiou meeting in 1889, Prof. Dr. T. C. Men- 

 (lenliall presented a series of observations of ball lightning, the concur- 

 rent testimony of which had convinced him of the reality of the phe- 

 nomenon. 



Lightning. — Mr. W. G. McMillan describes a lightning discharge 

 which struck a house in Calcutta. The instantaneous discharge of rib- 

 bon-lightning was apparently converted on entering the house into a 

 relatively slowly moving fire-ball. The effect is described as that of an 

 intensely brilliant ball of yellow fire about G or 7 inches in diameter 

 which passed across the room at a pace sufficiently slow to allow it to 

 be followed by the eye; about half way across, it a])[)eared to bo mo- 

 mentarily checked, and then, seeming to burst with a, deafening report, 

 which shook the whole house, it scattered and passed onward. A 

 large portion of the oxygen in the air immediately surrounding the 

 path of the flash was converted into the oxides of nitrogen. [Natin-e, 

 XL, p. 295.) 



Lightning conductors. — A discussion on lightning and lightning con- 

 ductors was held at the British Association meeting in 1888, in which 

 Professor Lodge, Mr. W. H. Preece. Lord liayleigh, Professor Forbes, 

 Sir William Thomson, and others participated. The discussion took 

 a wide range, though priiinirily designed to elucidate the question as to 

 the relative superiority of iron and copper wire. Mr. Preece stated 

 that both iron and copper are eflicacious. Sir V/illiam Thomson 

 knew of no experiment which proved iron less efficient, and it is prefer- 

 able because of its higher melting point as well as on account of its 

 cheapness. Contrary to the opinion of Mr. Preece, Professor Lodge 

 believed that lightning conductors are sometimes inefiicient even 

 when erected in accordance with all the demands of electrical science, 

 and, as a case in point, he instanced M. Melsen's hotel at Brussels 

 which had been struck and burned although elaborately protected. 



Terrestrial 7nag nctism.— Frof. Arthur Schuster has presented to the 

 Royal Society an elaborate investigation on the diurnal variation of 

 terrestrial magnetism, in which he makes Use of the method of har- 

 monic analysis to separate internal from external causes of variation. 



If the magnetic effects can be fairly represented by a single term in 

 a series of harmonics so far as the horizontal forces are concerned, 

 there should be no doubt as to the location of the disturbing cause, 

 for the vertical force should be in the opposite direction if the origin 

 is outside from what it should be if the origin is inside the earth. 

 If it be then a question simply of deciding whether the cause is 

 outside or inside, without considering a possible combination of both 

 causes, the result should not be doubtful, even if we have only an ap- 

 proximate knowledge of the vertical forces. He had previously shown 

 that the leading features of the horizontal components for diurnal 

 variations could be approximately represented by the surface har- 

 monic of the second degree and first type, and that the vertical vari- 

 H. Mis. 224 17 



