Intelligence and Miscellaneous Articles. 301 



equal to Tc (tan + $ sec 2 6) ; hence 



C'-C=Msec 2 0, 

 and 



C'_C Msec 2 6 a 2$ 



C & tan ft sin 6 cos sm20 



The error 2 must be expressed in circular measure ; if it be equi- 

 valent to a quarter of a degree, we have 



• C'-C ^ -00872 

 C sin 26 ' 



Hence we see, not only that when 6 is known the effect of the 

 error can be calculated, but also that the effect of a given error is 

 least when the deflection is 45°. 



The different forms of balance, determinations of specific gravity, 

 and the mechanics of solids, liquids, and gases occupy 110 pages ; 

 various experiments connected with sound, 16 pages ; the thermo- 

 meter, determinations of expansion, specific and latent heat, and 

 hygrometry, 58 pages ; experiments w 7 ith light, 100 pages ; and 

 the rest of the book (130 pages) is taken up with magnetism, elec- 

 tricity, and electromagnetism. The theories of the balance and 

 thermometer are given with unusual completeness ; and the chapter 

 on hygrometry forms a complete elementary treatise upon the sub- 

 ject. But perhaps the most important part of the book is that 

 which relates to electricity, in which full and clear instructions are 

 given for the comparison and measurement of currents, resistances, 

 and electromotive forces, capacities of condensers, and so on. It 

 should be noticed that the book is well up to date. Thus, for 

 example, we have, in the description of Carey Foster's method of 

 employing the B.A. form of Wheatstone bridge, an account of 

 Dr. Fleming's form of bridge, described in the Proceedings of the 

 Physical Society, and in this Magazine for May 1884. 



The sincere thanks of all teachers and students of Physics are due 

 to the Authors for their valuable book. 



XXXIII. Intelligence and Miscellaneous Articles. 



ON THE ELECTRICAL RESISTANCE OF ALCOHOL. 

 BY M. G. FOUSSEREAU. 



T EXAMINED the specific resistances of alcohol, and its mixture 

 •*- with water and with salts, by comparing them with the known 

 resistance of a pencil-mark drawn on a plate of ebonite. I used 

 M. Lippmann's method, and the experimental arrangement which I 

 employed in several previous researches *. Different specimens of 

 the absolute alcohol of commerce gave, at the temperature 15°, spe- 

 cific resistances comprised between 2-47 and 3*68 megohms. These 

 differences may, a priori, be ascribed either to the presence of a 



* Comptes Bendus, May 26 and July 15, 1884. 

 Phil. Mag. S. 5. Vol. 20. No. 124. Sept. 1885. Y 



