242 



SCIENCH. 



[Vol. I., No. 9. . 



This illustration presents in a forcible man' 

 ner the importance of giving the closest at' 

 tention to the protection of the 

 standards, where refined accuracy' 

 is sought. The influence of the 

 heat from the observer's bod^' is 

 frequently less than that "of other 

 causes against which protection is 

 supposed to have been made. 

 With a micrometer capable of 

 measuring with certainty a hun- 

 dred-thousandth of an inch, we 

 can repeat observations again and 

 again with a range not exceeding 

 this amount, and j-et the result 

 will,difier from that obtained on 

 another day bj* a quantity several 

 times larger than the extreme 

 range during a set taken all at 

 once. Any one who has made 

 careful linear or other compari- 

 sons will have noticed this. The 

 fact that the bars, while subjected 

 to apparently the same influences, _ 

 are j'et differentl3' affected, is the fT 

 principal cause of this trouble; ""_ 

 and the onlj- way of eliminating 

 the effects from the final result is 

 to so change and alternate the bars in position 

 as that the disturbing influences maj' operate 

 in turn on the one or the other of the standards 

 under consideration. H. W. Blair. 



which form enlarged ends to the latter, and 

 are marked g. In Fig. 19, which represents a 



section through half the ring, the method of 

 attachment and of coupling up is clearly shown. 

 On reference to Fig. 17, it will be seen that each 

 armature ring, G-, is built up of sixteen flat- 

 tened oval bobbins, H, separated from one 



HISTORY OF THE APPLICATION OF THE 

 ELECTRIC LIGHT TO LIGHTING THE 

 COASTS OF FRANCE.^ 



V. 



It onlj' remains now to describe the de Meri- 

 tens machine to complete the description of the 

 electric appliances for hght-houses. 



M. de Meritens has devised several types of 

 machines. Tlie one adapted for light-house 

 purposes, shown in Fig. 16, has the permanent 

 magnets of horseshoe form arranged radially 

 around the axis in a precisely similar manner 

 to the disposition of the field-magnets of the 

 old Alliance machine, which in general appear- 

 ance it at first sight much resembles. 



Fig. 17 is a transverse section of the machine, 

 and Fig. 18 a longitudinal section taken through 

 the axis, so as to show, in both views, the 

 armature ring, and the position of the field- 

 magnets with respect to it. 



Figs. 19, 20, and 21 show the details of the 

 armature bobbins marked H, the iron core- 

 pieces, h h, and the projecting pole-pieces, 



1 Concluded from No. 8. 



another by the projecting pole-pieces, g; and 

 around each ring are fixed, radially to the 



