390 



NATURE 



{March i8, 1875 



THE PROGRESS OF THE TELEGRAPH 

 I. 



IN the present day scientific research makes such rapid 

 progress, and produces such wonderful results, that 

 the mind ceases to appreciate the advancement, which 

 can only be realised by looking back, from time to time, 

 to ascertain what was the condition of any special branch, 

 any given number of years ago. It is only necessary to 

 retrace time some twenty-five years, and in almost every 

 department of practical science the step by step advance- 

 ment may be traced, from sewing machines to steam 

 hammers ; from lucifer matches to lighthouses. Rut, 

 perhaps, in no department of the applied sciences has 

 scientific research been productive of more valuable and 

 practical results than in the vast arena of electrical inves- 

 tigation ; and great as has been the progress made in 

 this department, still the knowledge obtained tends only 

 to point out the vast field of research open to the student 

 in discovering those fundamental laws and harmonies in 

 nature's laboratory at present concealed from our view. 



Sufficient, however, is already known in this special de- 

 partment of knowledge to inform us that electrical action 

 and activity enters largely into the constitution of the solar 

 system, regulating, in some degree at present not un- 

 derstood, the relation between the sun and our globe, 

 as regards various terrestrial phenomena; as v.-ell as 

 the disturbances upon the solar disc in relation to our 

 earth's terrestrial and magnetic currents, as demonstrated 

 in the daily deviations of the compass, and auroral dis- 

 plays in the regions adjacent to the polar latitudes of the 

 earth Thus we see that whatever may be the vast 

 field of research that remains to the student in this branch 

 of scientific investigation, most important results have 

 been developed. Time has been almost annihilated, and 

 in the race between the earth's revolution on its axis, and 

 electrical speech, man's inventive genius has been victo- 

 rious — time and space being so far distanced that in elec- 

 trical transmissions from one part of the globe's surface to 

 another, time has no value as measured by the earth's 

 rotation ; messages sent from India and the East 

 arriving hours before the time of their despatch. The 

 introduction of the electric telegraph is quite within the 

 memory of the present generation. Up to 1844 elec- 

 trical knowledge was more or less confined to the lecture- 

 table ; crude experiments upon friclional electricity and 

 the elements of magnetic and voltaic phenomena consti- 

 tuted the portfolio of knowledge as accepted by the public. 

 The profound researches of Oersted in 18 19 in relation to 

 the influence of a current of electricity upon the magnetic 

 needle is of great importance and may be summarised as 

 follows : — A magnetic needle poised on a pivot so as to 

 move freely in a horizontal plane adjusts itself in what is 

 termed the magnetic meridian. If a metallic wire is placed 

 parallel to the needle at a little distance above it, and a 





Fin. I — ^V^llon ui" an tilcciiical cuiiliu on Uic niagr.etic needle. 

 (Oersted's experiment.) 



current of electricity is passed through the wire, the mag- 

 netic needle will no longer remain parallel to the wire, but, 

 leaving the magnetic meridian, will set itself across the 

 current ; and the fame eflect will be produced if the wire 



is placed below the needle, and it will be found that if 

 the direction of the current in passing through the wire 

 is from S. to N., the north pole of ttie needle will be 

 deflected in an opposite direction to where the current is 

 passed from N. to S. ; in other words, when the current 

 passes horizontally over the needle, that pole which is 

 nearest to the negative end of the battery always moves 

 to the west, and when the current is passed under the 

 needle the same pole will deviate to the east. Ampere in 

 1820, who employed the magnetic needle, the coil of wire, 

 and the galvanic battery, to indicate signals, developed 

 the principles of the discovery of Oersted, and demon- 

 strated the fact that currents themselves exert an influence 

 on other currents. From the importance of Ampere's 

 experiments in relation to all telegraph apparatus, a few 

 words clearly illustrating the action of the current upon 

 the magnetic needle are necessary. 



If the observer regards himself as the conductor or 

 connecting wire placed parallel to the needle, and whose 

 face in every position is turned towards the centre of the 



Fig. 3, — Deviation to the left of tlte current. Lower current. 



needle, and the current from the positive pole of the 

 battery to the negative pole is supposed to enter his feet 

 and pass out at his head, the current will be found to 

 develop a right and left influence on the magnetic needle, 

 corresponding to the right and left of the person himself : 

 so that when an electric current acts on a mai^netic needle, 

 the south pole of the needle — which is that which is directed 

 tov/ards the north — is deviated towards the left. Figs. 2 

 and 3 illustrate this : for when the parallel current is 

 passed above the magnetic needle, the south pole .\ is 

 deflected to a' to the left of the current, or towards the 

 west ; and on the current being passed below the needle, 

 the same pole is deflected to a', being still to the left of 

 the observer, but in this case the pole a has moved to 

 the east. Ampere also demonstrated that when two 

 metallic wires are traversed simultaneously by an elec- 

 trical current, the wires are either attracted towards or 

 repelled from each other according to the relative direc- 

 tions of the two currents. Thus, when they move in the 

 same direction through the parallel wires, they attract 

 each other, while they repel each other if they move in a 

 contrary direction. Two non-parallel currents attract 

 each other, if both are approaching or receding from the 

 direction of the apex of the angle formed by the ends 

 produced, while they will repel each other if one of the 

 currents approach, and the other recedes from the apex 

 of the angle. Fig. 4 illustrates the three cases of attrac- 

 tion and two cases of repulsion to which these laws of 

 Ampere's refer. Ohm in 1827, who put forward his cele- 

 brated formuliE relating to the quantity of the galvanic 



