330 
POPULAR SCIENCE REVIEW. 
way beyond the ken of the observers. The writer would be glad to receive 
any facts that will prove whether any uniformity of direction is observable 
elsewhere, and that will, if so, lead to its explanation. 
A Horizontal Pendulum . — In u Poggendorffs Annalen,” C.L., p. 134, is 
described by Herr Zollner a series of experiments with a form of horizontal 
pendulum of such surprising delicacy that it seems to open a wide and 
fruitful field for investigation. This instrument consists of a short hori- 
zontal rod suspended by a vertical piece of fine watch-spring, and carrying at 
one end a heavy leaden weight and mirror. To prevent the other end from 
rising, a second watch-spring is attached, and fastened below. The two 
points of support lie therefore nearly in the same vertical, and are equi- 
distant, one above and the other below the pendulum. They are connected 
with the top and bottom of a vertical rod, which rests on a tripod, with 
levelling screws. If the two points lie in the same vertical, the weight will 
remain in any position ; but if one of the levelling screws is slightly moved, 
the pendulum will assume a position of equilibrium around which it will 
vibrate if disturbed. It will act, in fact, precisely like a common pendu- 
lum, except that the effect of gravity has been greatly diminished, so that 
the time of vibration is increased. Its sensibility is of course readily varied 
by shifting the levelling screw. In the instrument actually employed, the 
pendulum weighed about 6 lbs., and when removed from its supports 
and vibrated vertically like a common pendulum, its time of oscillation was 
about '25 of a second. The springs were about eight inches long, and the 
delicacy of the instrument was such that its vibrations were easily observed 
when the time was increased to thirty seconds, corresponding to a diminu- 
tion of the force of gravity of 14,000 times. 
The Effect on Induction Currents of the Condenser . — This is a paper which 
does not well bear abstraction. It appears in full in the “ Comptes 
Kendus.” While physicists generally admit that the spectral modifica- 
tions, produced by introduction of a Leyden jar into the induced circuit, are 
due to variations of the temperature, and not to any particular alteration in 
the physical nature of the discharge, he yet offers some remarks in support 
of this view : — 1. One may observe the thermal superiority of the condensed 
spark over the ordinary spark on comparing together the spectra obtained, 
under different conditions, by means of the same substance. 2. The effects 
of the condenser being due to increase of temperature, there is gradual 
passage from the spectra obtained with the aureole of the ordinary spark to 
those when a powerful Leyden jar is employed. 3. The action of the con- 
denser does not appear the same in different spectra. 4. The different lines 
of the same spectrum are not always equally affected by the condenser. 
5. The lines intensified by the condenser become nebulous and enlarged. 
6. The broadening of narrow lines at high temperature is explained by the 
perturbations undergone by the molecular movements, when the forces 
applied are considerable. 7. The lines of emission of solid or liquid sub- 
stances are nebulous. 8. It seems necessary to distinguish two kinds of 
continuous spectra proceeding from those of the second order, viz. (a), 
spectra, the lines of which are enlarged by increase of temperature ; ( b) f 
those the lines of which owe their enlargement to the little freedom of the 
molecules. If, as it seems, there is sometimes a gradual transformation of 
