28 KEPORT— 1870. 



Sir Thomas Maclear, it appears ttat the time elapsing between the time-current 

 leaving the Observatory at Cape Town and the receipt at Cape Town of the signal 

 announcing the falling of the ball is only -j'j- of a second. What is being daily done 

 in the Cape can, however, be best summed up by a short quotation from a letter 

 received from Sir Thomas Maclear, giving an account of the successful inaugura- 

 tion of this signal. After detailing the general arrangements, Sir Thomas goes on 

 to state : — 



" A few tentative signals having proved satisfactory, the ' preface ' was issued 

 from the Observatory at ten minutes before one o'cIock, and at the instant of one 

 o'clock the Observatory time-ball clock closed the circuit, discharging the Obser- 

 vatory ball, the Simon Town ball, twenty-four miles distant, the Cape Town time 

 gun, three miles distant, and the Port Elizabeth ball, distant 500 miles." 



On the Mode of Action of Lightning on Telegraphs, and on a Neiv Method of 



constructing TeJegraph-coils. By S. Alfred Yaeley, Assoc. Inst. C.E. 



The author stated that in the early days of electric telegraphy lightning-protec- 

 tors were used to protect the coil-wires in telegraph offices ; the general type of the 

 protector adopted was an insulated pointed conductor connected to the line-wire, 

 and in close proximity to a metallic conductor leading to the earth. At a subse- 

 quent date the use of lightning-protectors in telegraph offices was practically aban- 

 doned, as they were fomid not to prevent the fusion of the coil-wires, or only 

 exceptionally ; for although the lightning would leap across the space of air sepa- 

 rating the insulated conductor from the earth-conductor, an electrical discharge 

 also passed through the coils and frequently fused them. 



When lightning-storms occur in the neighbourhood of telegraph-wires, although 

 the wires may not be actually struck, powerful currents are induced in the wires ; 

 these currents may in some cases be sufficiently strong to fuse the instrument coils, 

 but they more frequently simply demagnetize, and as often reverse the magnetism 

 of the magnetic needles which are situated in the coils of needle-telegraph instru- 

 ments. 



Needle telegi-aphs are largely used on railways for train signalling, and the de- 

 magnetization or the reversal of the magnetism in these instruments is very serious, 

 as the safety of the train depends in a great degree upon the correct working of the 

 signalling instruments. In 1866 the author introduced instruments which he con- 

 siders to fulfil in a great degree the conditions to be desired in needle telegraphs. 

 In these instruments the case, the bearings, and the blocks which limit the motion 

 of the handle are made of cast iron in one solid piece, so there are no parts to be 

 shaken loose by rough usage. The magnetic needles inside the coils, instead of 

 being made of tempered steel magnetized, are made of soft iron, and are rendered 

 magnetic by induction from permanent magnets in the neighbourhood of the coils ; 

 and as they are magnetic only by virtue of the permanent magnets in their proxi- 

 mity, the influence of powerful currents induced by lightning can only be momen- 

 tary. 



The coils are protected from fusion by means of a novel protector termed a 

 "lightning-bridge," as it forms a bridge for high tension electricity to pass over. 

 It was well known that high tension electricity would leap across a small space of 

 air in preference to passing throughout the length of a coil of wire ; and it was 

 stated this arose from the momentary resistance the wire opposes to polarization 

 or magnetization, — a resistance probably approaching to infinite resistance during 

 an infinitely small interval of time ; and from this cause, even in a vacuum protec- 

 tor, where the pointed conductors are enclosed in an exhausted chamber, the 

 main discharge will leap across a space of air separating the insulated conductor 

 and the earth conductor outside the exhausted chamber. The author, when expe- 

 rimenting with electric currents of varjdng degrees of tension, observed the very 

 great resistance which a loose mass of powder of conducting matter opposed to 

 the passage of electricity of moderate tension ; he found with a tension of 50 

 Daniell cells electricity did not pass through a loose mass of finely divided black- 

 lead or wood charcoal. When the tension was increased to two or three hundred 

 cells, the particles aiTanged themselves by electrical attraction, making good elec- 



