Intelligence and Miscellaneous Articles. 163 



fering with the idea of the action above explained. We may in 

 fact suppose them merely portions of the aether. 



Perhaps it may be objected that my conductors are not circuits ; 

 but a current which keeps passing backwards and forwards from 

 a condenser acts in precisely the same manner as a true current 

 (see art. 776 Maxwell &c), and why not also without the con- 

 denser? 



Note. — Perhaps this idea is nothing new, and has occurred to 

 others as well as to me. I have been told, however, that C. Maxwell 

 himself would never precisely define the action by which he sup- 

 posed light and electromagnetic induction propagated. 



ON A NEW APPARATUS FOR MEASURING ELECTRIC CURRENTS. 

 BY M. DE LALANDE. 



The apparatus for measuring electrical currents based on the use 

 of magnetic needles or of permanent magnets are known to be 

 largely influenced by the variations in the terrestrial magnetism, as 

 well as by variations in the magnetic conditions of the magnets 

 themselves. The data furnished by instruments of this kind which 

 are provided with a fixed graduation in amperes or volts, can only 

 be guaranteed when their standard is verified at close intervals. 

 This is a serious inconvenience, especially for industrial applica- 

 tion, for which these instruments have the great advantage of 

 giving direct and continuous indications. 



The amperemeters and voltmeters which I have the honour to 

 exhibit to the Academy have no permanent magnets in their con- 

 struction, and therefore are free from the source of errors just 

 mentioned. They depend on the actions exerted by a solenoid on 

 a bundle of soft iron wires movable in the interior, and kept by an 

 antagonistic force. They belong to the type of M. Becquerel's 

 electromagnetic balance, and like this instrument enable us, so to 

 speak, to weigh the electrical action of currents. 



The apparatus, which might be called an electrical areometer, 

 consists of a bundle of soft iron wires placed inside a metal 

 areometer which is immersed in a glass cylinder full of water, and 

 round which is coiled the wire through which passes the current to 

 be measured. The original position of the areometer (regulated by 

 the level of the liquid, which is kept constant) is always the same ; 

 it will be seen that it will take a position of equilibrium by sinking 

 to a certain depth, which varies with the strength of different 

 currents which traverse the bobbin, but which is constant for the 

 same strength. The top of the stem of the areometer is fiat, and 

 forms the index, which runs along a vertical scale graduated experi- 

 mentally. An important peculiarity is the guiding of the stem of the 

 areometer, which passes through a metal eye in the interior of the 

 liquid. This arrangement suppresses friction against the sides of 

 the cylinder and does not alter the sensitiveness of the instrument. 



By varying the dimensions of the bobbin, and those of the 

 bundle of soft iron wires or of the stem of the areometer, we can 



