332 Intelligence and Miscellaneous Articles. 



sufficient certainty, and especially whether the quantity /z proves to 

 be independent of h, equation II. For this end three experiments 

 were carried out, in which 



m — 2'2 grins. 



M+w=300grms. 



<7=981 centims. 

 The results were : — • 



For 7? = 28 centims. 



1. <r=112, =112-3, and =112-8 centims.; mean= 112-3 centims. 



For h=25 centims. 



2. <r = 86-6 or 86*8 or 87'2; mean =87 centims. 



For 7i=23 centims. 



3. ff==81; mean =81. 



According to formula II., from 1, /*=0*80 centim.; from 2, 

 ^=0-88 centim.; from 3, /z=0*88 centim. 



In further experiments the amount of the friction itself was 

 ascertained. According to the arrangement of the machine, 24 

 inches descent =65 centims. ; therefore 362-21 inches corresponded 

 to the acceleration of gravity. The overweight m= 1*514 was 



3 vi 1 _ am 



chosen so mat v, ^ = i5n> ancl consequently jrrj— =2*415 



inches fall. 21*732 



With h=9 inches, a =25 inches fall, and 2^= . . 



From equation III., x was now found =0*21 grm. We will call 

 this weight the friction-iv eight. 



In another experiment the friction of the pin of the wheel in its 

 socket was increased by means of screws ; and there resulted, 

 under otherwise like circumstances, for h = 9, (7 = 16*5 inches fall, 

 ,r=0*300. 



Both experiments were in perfect accord with the calculation. 

 The friction- weights I made of tinfoil, of the form of the usual 

 fall-weights. 



In order to make use of the method of friction-determination 

 conveniently, it will be prudent to construct a Table, and to calcu- 

 late the friction-weights with equal g . -jrfr— - and h within certain 



limits of <T. For various reasons it is unnecessary to actually draw up 

 such a Table here. — PoggendorfPs Annalen, vol. cxlix. pp. 122-126. 



A REMARKABLE INTERFERENCE-PHENOMENON OBSERVED BY 

 M. SEKULIC. 



I was sitting one evening opposite to a looking-glass. Happening 

 to cast a glance into it, I noticed on my head splendidly coloured 

 interference-streaks. On more attentively considering the circum- 

 stances which might occasion them, I remarked in the mirror three 



