776 
Notes . 
A new thermo-electric battery has been invented by M. Clamond 
for the production of the electric light. With a consumption of 
9^ kilos, coke, a current is produced capable of maintaining four 
lamps, each equal to twenty-five Carcel burners. 
In the American “ Quarterly Microscopical Journal ” Mr. F. H. 
Wenham gives some useful information relating to practical 
methods of obtaining parabolic forms. The mode of forming 
the template is simple and ingenious : — A cone of hard wood or 
metal is turned, removed from its centre, and fastened by one of 
its sides on a suitable chuck ; a section is made in the lathe 
parallel to the attached side ; a piece of accurately flattened 
brass, somewhat larger than the section, is fixed to the portion of 
the cone by screws, and above that a piece of similar material to 
that from which the cone was turned ; it is then returned to its 
centre, and the cone turned down to its original form : the metal 
plate has its edges finished by holding to it a “dead smooth 
file.” The cone is unscrewed, and the brass plate comes out a 
true parabola. The block of glass is turned with an old saw file 
and plenty of turpentine until it approximately fits the template ; 
the paraboloid is then turned with a keen edge until the template, 
smeared with reddle and oil, marks it evenly all over ; the marks 
are ground out with a small block of brass and emery of gradu- 
ated fineness, until all scratches disappear. The glass is polished 
with a buff stick and crocus and water, and finally a piece of hard 
bees’ wax is held against it, with finer crocus, to obtain the last 
degree of polish. If che paraboloid be a non-immersion one, 
with a cupped top, it may be turned flat on the end until the re- 
quired thickness is arrived at, and the hemispherical cavity 
roughly turned out to a half-circle template till the centre is 
brought to the focus : the cavity is then finished in the same way 
as a concave lens. Finally, when rotatory in the lathe, the 
paraboloid is perforated through the axis with a steel drill and 
turpentine. 
A new “ Catalogue of Electric Apparatus ” has been issued by 
Mr. E. Paterson, Bedford Court, Covent Garden. This Cata- 
logue has the double merit of being copious and well illustrated 
with nearly 160 woodcuts. The first part contains a priced list 
of apparatus used for instruction and demonstration, while the 
second deals entirely with practical matter or applied electricity. 
In the second part a clear description is given of the construction 
of electrical apparatus intended for house signalling, bells, tele- 
graphing short distances, &c. The telephone and electric lamp 
are also described. The directions given for fixing electric house- 
bells are sufficiently clear and devoid of technicalities to be of 
service to any ordinarily intelligent builder or bellhanger. 
