24 REPORT — 1855. 



mode proposed by the author. No less thaa eight currents — four positive and four 

 negative — were in this way transmitted in a single second of time through the same 

 length of wire (1125 miles), through which a single current required a second and 

 a half to discharge itself spontaneously upon the paper. Having stated the precau- 

 tions adopted to guard against error in the observations, the details of the experi- 

 ments were then concisely given, including those for " velocity," which showed a 

 much higher rate attainable by the magneto- electric than by the voltaic current. 

 The author then recapitulated the facts, to which he specially invited attention : — 

 First, the mode of testing velocity by the use of a voltaic current divided into two 

 parts (a split current), one of which shall pass through a graduated resistance tube 

 of distilled water, and a few feet only of wire, while the other part shall be sent 

 through the long circuit, both being made to record themselves by adjacent styles 

 upon the same slip of electro-chemical paper. Second, the use of magneto-electric 

 " twin-currents," synchronous in their origin, but wholly distinct in their metallic 

 circuits, for the same purpose, whether they be made to record themselves direct 

 upon the paper, or to actuate relays or receiving instruments which shall give con- 

 tacts for a local printing battery. Third, the effects of induction, retardation of the 

 current, and charging of the wire, as shown autographically ; and contrasted with 

 this — fourth, the rapid and forcible discharging of the wire by the use of an opposite 

 current; and hence — fifth, the use of this as a means of maintaining, or restoring at 

 pleasure, the electric equilibrium of the wire. Sixth, absolute neutralization of 

 currents by too rapid reversal. Seventh, comparison of working speed attainable in 

 a given length of wire by the use of repetitions of similar voltaic currents as con- 

 trasted with alternatirig magneto-electric currents, and which, at the lowest estimate, 

 seemed to be seven or eight to one in favour of the latter. Eighth, proof of the 

 co-existence of several waves of electric force of opposite cheu^acter in a wire of given 

 length, of which each respectively will arrive at its destination without interference. 

 Ninth, the velocity, or rather amount of retardation, greatly influenced by the 

 energy of the current employed, other conditions remaining the same. Tenth, no 

 adequate advantages obtained in a 300-mile length by doubling or trebling the mass 

 of conducting metals. The author, in conclusion, stated his conviction, that it 

 appeared from these experiments, as well as from trials which he had made with an 

 instrument of the simplest form, actuated by magneto-electric currents, that the 

 working speed attainable in a submarine wire of 1125 miles was ample for commer- 

 cial success. And may we not, he added, fairly conclude also, that India, Australia, 

 and America, are accessible by telegraph without the use of wires larger than those 

 commonly employed in submarine cables ? 



On the New Maximum Thermometer ofH. Negretti atid Zambra. 

 Communicated hy C. Greville Williams. 



The very simple but effective instrument for indicating maximum temperature, 

 invented by Messrs. H. Negretti and Zambra, is remarkable both for the delicacy of 

 the workmanship and for the diflBculty which is found in constructing it, a difficulty 

 which is entirely of a practical character, and prevents the possibility of a perfect 

 instrument being constructed by any but a dextrous artist. 



It consists of a thermometer-tube bent near the bulb, in the manner of the old 

 ones, but just at the bend the tube has an impediment caused by a contraction at 

 that point. This choking of the tube is insufficient to prevent the easy passage of 

 the mercury during its expansion, but nevertheless effectually prevents its return as 

 the temperature falls, and the mercury in the globe consequently occupies less 

 space. The portion left in the stem serves as the index of the highest temperature 

 arrived at. 



It is acknowledged that a certain amount of error is here unavoidably introduced, 

 from the fact that the mercury at the time of passage into the tube is at a higher 

 temperature than when the observation is made, and occupies a larger space in the 

 tube. Consequently, the instrument when read off indicates a lower temperature 

 than the truth ; but although this objection may justly be made on theoretical 

 grounds, in practice the eft'ect of this error on the result is inappreciable, owing 

 to the very small quantity of the mercury in the tube. 



