12 Professor Tyndall [Jan. 17, 



As regards lighthouse illumination, the next step forward was 

 taken by the Elder Brethren of the Trinity House in 1876-77. 

 Having previously decided on the establishment of the electric light at 

 the Lizard in Cornwall, they instituted at the time referred to, an elabo- 

 rate series of comparative experiments wherein the machines of Holmes, 

 of the Alliance Company, of Siemens, and of Gramme, were pitted 

 against each other. The Siemens and the Gramme machines delivered 

 direct currents, while those of Holmes and the Alliance Company 

 delivered alternating currents. The light of the latter was of the 

 same intensity in all azimuths ; that of the former was different in 

 different azimuths, the discharge being so regulated as to yield a gush 

 of light of special intensity in one direction. The following table gives 

 in standard candles the performance of the respective machines : — 



Names of Machines. Maximum. Minimum. 



Holmes 1523 .. .. 1523 



Alliance 1953 .. .. 1953 



Gramme (No. 1) 6663 ,. .. 4016 



Gramme (No. 2) 6663 ,, .. 4016 



Siemens (Large) 14818 .. .. 8932 



Siemens (Small, No. 1) 5539 .. .. 3339 



Siemens (Small, No. 2) 6864 .. .. 4138 



Two Holmes's coiiplfd 2811 .. .. 2811 



Two Gramme's (Nos.l and 2).. .. 11396 .. .. 6869 



Two Siemens' (Nos. 1 and 2) .. .. 14134 .. .. 8520 



These determinations were made by Mr. Douglass the engineer-in- 

 chief, and Mr. Ayres the assistant engineer of the Trinity House. 

 It is practically impossible to compare photometrically and directly 

 the flame of a candle with these sun-like lights. A light of inter- 

 mediate intensity — that of the six- wick Trinity oil lamp — was there- 

 fore, in the first instance, compared with the electric light. The 

 candle power of the oil lamp being afterwards determined, the intensity 

 of the electric light became known. The numbers given in the 

 table prove the superiority of the Alliance machine over that of 

 Holmes. They prove, for the resistances involved, the great superiority 

 both of the Gramme machine and of the small Siemens machine over 

 the Alliance, while the large Siemens machine is shown to yield a 

 light far exceeding all the others. The coupling of two Grammes, 

 or of two Siemens together, which was first successfully accom- 

 plished at the South Foreland, was followed by a very great augmen- 

 tation of the light, rising in the one case from 6663 candles to 11,396, 

 and in the other case from 6864 candles to 14,134. After this contest, 

 which was conducted throughout in the most amicable manner, 

 Siemens machines of the smaller type were chosen for the Lizard.* 



We have machines capable of sustaining a single light and also 



♦ As the result of a recent trial by Mr. Schwendler, they have been also 

 chosen for India. 



