SCIENTIFIC SUMMAEY. 
681 
wlio experimented Avitli a number of substances, found that the emissive 
power of oxide of copper was about ten times that of gold ; and that the 
emissive power of platina was between that of the oxide of copper and gold, 
but nearer to that of the latter. The emissive power of the oxides of zinc 
and iron is much greater for heat than for light. This is to be expected, from 
the fact that a number of invisible rays exist ; and the thermoscopic power 
includes all the rays, while the photometric includes only those which are 
visible. When the emitted rays are joined with rays derived from reflection 
or diffusion, their polarity is affected. 
JVeit/* Mode of employing Bunsen^s Battery. — M. Duchemin, not long since, 
announced to the Academy of Sciences that in a Bunsen’s battery the nitric 
acid could be replaced by percliloride of iron, and the sulphuric acid by a 
solution of common salt. He has now' stated that by substituting crude 
chloride of potassium for the common salt, the electro-motive force of this 
battery is increased, and its caloric effects intensified ; the electric light being 
easily produced when the chloride of potassium is employed, instead of 
chloride of sodium. 
An improved Seismometer or Earthquake Measurer. — Lieut.-Col. Eamstedt, 
of Helsingfors, has constructed a new form of seismometer, for which he pro- 
poses the descriptive name — Telegraph of the accidental movements of the 
earth. Considering that these movements are much more frequent and 
continuous than is commonly supposed, and that the greatest number escape 
notice through want of proper observation, he suggests that his instrument 
should be placed in the principal magnetic observatories of Europe, and other 
parts of the wmrld, where, being self-recording, it would note the occurrence 
of every shock or movement, however slight. If, as Lieut.-Col. Eamstedt 
remarks, there are tremblings of the earth nearly every day, it seems 
desirable that some notice of them should be taken ; and, perhaps, 
established observatories w^ould be the best places for the investigation. 
As all the records would have to be sent to one central office, the 
localities in which shock’s and tremblings are most frequent would be dis- 
covered ; and, in course of time, some conclusions might be drawn as to 
Avhether the movements are periodical, or form part of some intermittent 
system of vibrations by which the earth is affected. The seismometer is so 
constructed as to indicate, by lines traced with a pencil, the time at which a 
shock takes place, and its force and direction. 
The Spectrum of the Electric Spark. — The indefatigable Abbe Laborde has 
made some important observations upon the spectrum of lightning, which are 
reported in our contemporary. The Reader. When the flash appears directly 
before the spectroscope, as he has been fortunate enough to see it three or 
four times, the bright lines of which the spectrum is composed are very 
numerous and well marked. jMore often the lightning is seen reflected from 
the clouds in its spectrum, the bright Imes are still visible, and increase in 
number as the flash is more vivid. They are all of a dull white or lead colour, 
but one among them is always more apparent than the others, and is some- 
times seen alone. This line is not far from Fraunhofer’s line E. When, how'- 
ever, the flash appears at a great distance, or is seen through a thickness of 
cloud, almost all the bright lines disappear, and the spectrum is nearl}^ con- 
tinuous. The appearance is similar to that observed when several unpolished 
