332 Application of Photography to the Self-registration 
the surface of the paper; when a less quantity of iodid is used, 
the paper appears to have a neutral tint: in this case, the beginning 
of the trace can sometimes be with difficulty developed. The 
greatest care must be taken not only to prevent the least inter- 
mixture of substances, and to confine each vessel, and each cloth, 
as well as each brush strictly to one use, but also to wash all the 
brushes very carefully in pure water after use, not only for their 
preservation, but because the presence of deposit from old solu- 
tions, even of the same kind, has an injurious effect. 
A room of 12 x 15 feet is all that is absolutely needed for a sin- 
gle instrument. It will be found very desirable to have a small 
cistern of soft water in it, provided with a stop cock, and witha 
sink and waste water pipe attached; the sink should have a lid 
to allow the paper to be kept in darkness, when convenient, with- 
out darkening the room: if to this we add two or three broad 
shelves, or small tables and conveniences for washing the hands, 
its equipment will be complete. 
he future comparison of traces will be greatly facilitated if 
they all include the same period of absolute time. Each register 
at Toronto begins at 2U’ after 6° of Géttingen mean time, and 
terminates at 6° 0@ of the following day, being nearly at Toronto 
n. 
“ A continuous registration of the variations of the thermome- 
ter has been obtained by intercepting the focal line of light formed 
on the paper, by the stem of a thermometer having a wide flat 
bore, a sufficient quantity of light passes through the empty por-* 
tion of the bore to darken the paper, but it is entirely excluded 
from the portion occupied by the mercury. The register, there- 
fore, consists of alight and dark space, separated by a well de- 
fined boundary line the distance of which from the base line will 
furnish the required indication. This particular application of the 
apparatus, prefers no claim to novelty, as a very similar means of 
registering the variations of the thermometer has been already 
published, (Engineer’s Magazine, Nov., 1845,) and is here intro- 
duced merely as forming a necessary part of a complete automa- 
tic meteorological registration.” 
Allusion has been made at the commencement of this article, 
to the action of light upon silvered plates, as one of the modes 0 
effecting the self-registration of magnetical instruments. The 
apparatus referred to is the invention of Mr. Ronalds, and al- 
though capable of employing either paper or metallic surfaces, 18 
properly designed for the latter, and is essentially a daguerreoty pe- 
An instrument on this principle was sent from England for the 
agnetic Observatory in August last, but by accident to the ves- 
sel, has not yet been received there, and cannot now be brought 
into operation before June, 1850. It is intended to register the hor- 
izontal force, and differs essentially in many respects from the ap- 
scanned 
