TRANSACTIONS OF THE SECTIONS. 13 



0)1 a recent Description of an Iris seen in the Lake of Lucerne. 

 By Mx. J. J. "Walker. 



In a letter which appeared in the 'Athenaeum' of September 3, the writer described 

 the appearance of a splendid solar rainbow, and its " reflected image " in the Lake 

 of Lucerne. This was an instance, seen imder very favoiu'able circumstances (from 

 the calmnesa of the water, the low altitude of the sun, and the elevation of the observer 

 above the siuface of the lake), of that secondary iris, to the rationale of which the 

 author had drawn the attention of the Section at the Aberdeen Meeting, 1859. 



Electeicitx. 



Description of a Clieap Form of Automatic Regulator for the Electric Light. 



By Samuel Highlet, F. G.S. 

 The principle of this " Pneumatic Electric Eegulator " was suggested to the 

 author by Mr. Maiden. The instrument is sensitive in action, and, from its 

 simplicity, little liable to get out of order, and can be arranged for any length of 

 carbon. The rod supporting the upper carbon is attached to a copper float, which 

 rests upon a colunm of water, contained in a chamber communicating by an opening 

 with an air-chamber, from which a pipe, terminated by a flexible tube of vulcanized 

 rubber, is carried imder a wedge-shaped piece attached to the rod holding the lower 

 carbon, and which passes through a coil of stout insidated wire. ,"When the carbons 

 are brought into contact, the current passes through, and the coil becomes magnetic, 

 pulls down the ii'on core, and separates the carbons, so as to produce the proper 

 arc of light, at the same time forcing down the wedge upon the flexible tube, 

 closing it as eflectuaUy as with a stop-cock. As soon as the distance between the 

 poles becomes too great for the cm-rent to pass freely, the coil ceases to be magnetic, 

 and the lower rod is raised slightly by means of a lever and countei-poise spring. 

 Air is thus forced from the chamber by the column of water ; the float sinks, 

 bringing down the upper carbon into contact with the lower one : the cm'rent is 

 thus again completed ; the coil becomes magnetic, and pulls down the iron core, 

 pressing the stop-cock wedge upon the rubber tube. These operations are repeated 

 sympathetically as the carbon bm-ns away. 



On the Retardation of Electrical Signals on Land-Lines. 

 By Pleeming Jenkin-. 



The retardation of electrical signals through submarine cables has been studied 

 closely for some years ; but on land-lines, owing to the difficulty of the experiment 

 and small influence of the retardation on the signals usually employed, little atten- 

 tion has been paid to the phenomenon. The invention of automatic instruments, 

 such as Prof. Wheatstone's transmitting 

 signals, which succeed one another with 

 great rapidity, now renders the retardation 

 an important element of calculation, even 

 on the common aerial lines. The electi-ic 

 current is never received at a distant sta- 

 tion at the very instant of its transmis- 

 sion ; it arrives gradually, as represented 

 in the annexed curve, in which the hori- 

 zontal ordinates represent the times after 

 the cfrcuit has been completed in terms 

 of a quantity a ; while the vertical ordi- " 

 nates represent the relative strengths of the current at each moment : thus on 

 any circuit the received cm-rent will have reached about 65 per cent, of its whole 

 strength after a period of 6a. The quantity a varies with the circumstances of each 



case, and is equal to -^log^^^gj, where A=the resistance of the conducting wire 



