268 Mr. Abraham on New Pha:?iomena caused by 



ning,") observes, that "when lightning falls on a lightning-rod, 

 it frequently happens that a small portion of the point is fused ; 

 and this effect is not very different to what may be produced 

 by large electrical batteries." Hence we presume that a 

 pointed rod which has been a long time erected, may have lost 

 much of its original conducting power, owing to its pointed 

 end having become oxidated from electrical and other at- 

 mospherical causes, and consequently become knobbed or 

 rounded at the upper end ; and as the safety of the building 

 depends upon the sile7it and rapid transmission of the electric 

 fluid into the earth, particularly when the charge of the de- 

 scending fluid is great, 1 should recommend that the upper 

 part of all conductors of lightning be made of steel properly 

 hardened and tempered, to hold concentrated at the point the 

 greatest magnetic power that can be given to the rod ; and well 

 gilt at the point, to preserve it from the action of the atmo- 

 sphere. This conductor, from the preceding experiment, would 

 receive the approaching accumulated electrical fluid at a much 

 greater distance than an equally fine nonmagnetical rod ; 

 whereby its discharging power upon that conductor would 

 be greatly diminished, and the building rendei'ed more safe 

 from the effect of the destructive element. 



The 42nd Number of the Journal of Science and the Arts, 

 contains an interesting paper, by Lieut. Johnson, R.N., " On 

 local and electrical influences on compasses." 



After havmg attentively read the paper, I felt so much in- 

 terest in several of the experiments, that I was induced to try 

 whether those which the Lieutenant asserts " produced a 

 variation of the needle in the compass-box, by wiping the 

 glass cover with a silk handkerchief or other soft substance," 

 were correct. In the course of these experiments I noticed 

 several phaenomena which the Lieutenant seems not to have 

 been aware of at the time his paper was written. He remarks, 

 " that having observed a considerable deviation produced oh 

 the compass needle by the mere act of wiping the dust from 

 the glass cover of the compass-box with a silk handkerchief, 

 I rubbed it successively v/ith silk, woollen, cotton, and linen, 

 and found that they produced similar results, and also leather 

 in a less degree, viz. causing a considerable deviation, generally 

 to the eastward, sometimes as much as 20°, and once to 40°, 

 from the magnetic meridian." After repeating this experi- 

 ment several times, I was not able to discover, when the com- 

 pass needle was placed due north and south, and the box 

 containmg the needle was kept firmly in its place during the 

 experiment, that the friction produced any variation whatever. 

 He further observes, " thai one pole of the needle adhered 



for 



