130 Progress in Science. (January, 
but it has no effe@ on anything else. Prof. Clerk Maxwell said that the 
method seemed capable of furnishing very good results, and was well worth 
putting into operation. He said, also, that the change of resistance at the 
commutator was entirely eliminated, but that the change of E.M.F., due to 
heat at the contacts, was not; however, Prof. Lorenz had used a revolving 
commutator and had not been much troubled by this effe&, and he got rid of 
what little there was by reversing the current in different experiments. The 
commutator must be accurately made, so as to cut off the current a definite 
proportion of each revolution. Prof. Wiedemann said it would be important 
to measure the area of the revolving coil accurately, and this, he thought, 
might be found the most difficult part of the experiments. Prof. Maxwell 
then explained a contrivance he had devised for ascertaining the dimensions 
of large coils, by letting a wheel (on whose axle a string could wind itself) 
roll on the wire as it was wound on, and afterwards running this wheel along 
a scale till the string was unwound. The length of the wire and number of 
turns is thus known, and from these the effective area of the coil is easily 
found. Prof. Maxwell further suggested that the commutator should only 
make contact for a very short time in each revolution, as this would do away 
with any self-induction (or extra currents) which might take place if contac& 
were made long enough for the current to vary much in intensity. 
Mr. S. M. Yeates, the excellent philosophical instrument maker, in Dublin, 
has invented a most important modification of the step-by-step telegraph. 
In all alphabetical telegraphs hitherto made it is essential that the operator 
should always move the handle round in one forward direétion, and therefore, 
if a letter be required which precedes the one last indicated, it is necessary to 
carry the pointer all the way round the dial in order to indicate the letter 
required; if, for instance, the word ‘“‘ day” be transmitted, the operator 
moves the index from zero to D, passing over A, B, and C; having thus 
passed A, it hecomes necessary to go all round the dial to arrive at A, and 
having passed Y must again go round the whole alphabet before the word is 
completed. As each letter passed by the transmitting instrument sends a 
current which actuates the receiving instrument, and makes its index perform 
the same motion, it follows that, in transmitting this little word “ day,” there 
are no less than 49 currents sent along the line, and, as any one of such 
currents may miss, there are 49 chances of the instrument ‘‘tripping,” as it 
is called. In Mr. Yeates’s new instrument both the transmitting and receiving 
instruments work backwards or forward indifferently, and therefore—in the 
case supposed of the word ‘‘day”—the operator, having moved the 
index to D, has only to move it back to A, and then back to Y, thus trans- 
mitting the word with only eleven contacts, instead of forty-nine as in the 
other cases. The great advantage gained by this will at once be seen :— 
First, it greatly increases the speed of the instrument; and secondly, it greatly 
lessens the chances of tripping. 
M. Gaiffe has devised apparatus used to light the chandeliers of the Paris 
National Assembly Hall. The hall is lighted by means of chandeliers con- 
taining 256 burners. To each chandelier a wire conduéts the electric charge, 
but the return currents traverse a single cable to which all the wires converge. 
Each wire at the battery end—or rather induction coil end—starts from a 
separate insulated metallic button, which are put in communication with the 
secondary wire of the coil by means of an excitor terminated by a ball, and 
attached to the coil by a chain; the other end of the coil’s secondary wire is 
is in connection with the return cable. The wire starts from the button and 
terminates at the burner; it resumes its course onward to the return cable, 
the circuit being complete, with the exception of a small breakage at each 
burner. Tolight the hall, the coil is first worked; then the gas is turned on, and 
the excitor applied to the several buttons causes sparks to be emitted at each 
burner, and thus enflames the escaping gas. 
M. Charles Vavin has invented a magneto-mechanical sorter. Its object 
is to mechanically separate iron chippings and dust from the copper found 
mixed with the detritus and filings of factories. This sorting is ordinarily 
