82 Reply to Mr. De la Rue’s remarks on the N. Spencerit. 
Walker’s conclusions respecting the velocity are by no means 
inconsistent with Wheatstone’s experiment ; for the tension of the 
electricity and the conducting power and size of the wire differ 
so much in the two cases as to prohibit any comparison. Fizeau’s, 
on the contrary, stand in the directest opposition to it, for he 
finds that neither the tension of the transmitted electricity, the 
intensity of the current, nor the size of the conductor, exerts any 
influence on the velocity; and at the same time’ makes the 
velocity through his copper wire to be 110,000 miles a second, 
while Wheatstone found 288,000 to be the minimum limit of the 
velocity through the copper wire which he used. 
‘ (To be continued.) 
Arr. VIl.—Reply to Mr. De la Rue’s remarks on the Navicula 
Spencerii contained in the American Journal of Science, Vol. 
IX, p. 23; with a notice of two new test-objects ; by J. W. 
Battey. | 
In consequence of absence from home and long continued 
illness, I have been compelled to delay my reply to the remarks 
by Mr. De la Rue upon the subject of the Navicula Spenceril. 
I trust however that it is not too late for a few words in answer. 
Mr. De la Rue now admits that the American observers were 
right in attributing the appearances seen on these shells to rows 
of prominences, and not to perforations or depressions as stated 
in Mr. Queckett’s Treatise, (p. 440,) and as the larger figure on 
Plate 9 of that work represents them. As we agree with re- 
gard to the structure of these objects, the only remaining points 
of difference between us are the measurements of the distance 
between the rows, and the difficulty of the species as a test- 
object. With regard to the accuracy of my measurements it 
was impossible for me to judge, as Mr. De la Rue’s were not 
by Mr. De la Rue, I find that my measurements constantly differ 
from his, and always in the same direction and amount. AS 
manipulation, I can only conclude that our scales of « 
