My continued instructive correspondence with Dr. Lloyd on the subject 
was very profitable, and new arrangements were in consequence contem- 
plated which were applicable to either plan (viz. that of using a detached 
lens as heretofore, or an attached lens with deflectors, &c.), for comparing 
them at Kew; and Mr. Ross received some final instructions as to the work 
to be executed. 
But in the course of Mr. Ross’s operations in December, a considerable 
improvement occurred to me in the management of the light, viz. that of 
suppressing the condensing lenses at the object-end of the camera, bringing 
the index much nearer to the lamp, and employing the focus lenses to pro- 
cure not only a distinct image of the index, but also a brilliant pencil of 
light (broad enough for owr purposes) immediately from the flame itself. 
By these means the time required to produce the desired effect upon the 
paper was very considerably reduced. Mr. Malone assisted me in these ex- 
periments zealously. 
Several improvements were also made in the construction and disposition 
of the time-piece (vide Plate II. K), &c.; and at about this time, after 
many vain attempts, an improvement in the brilliancy of the flame itself was 
effected by a modification of Count Rumford’s “ Polyflame Lamp,” of three flat 
wicks, &c., and an especial adaptation of a high square copper chimney, &c. 
(vide Plates II. and IIT. D). 
The reason for not instituting the above-mentioned comparison of lenses, 
was chiefly that of finding the expense of a lens properly adapted to the 
purpose very considerable. Yet I trust that my anxiety to carry out prac- 
tically Dr. Lloyd’s important suggestions, combined with the occurrence of 
more favourable circumstances, may not be ultimately unavailing, or that 
some less costly method than we thought of may be propounded. 
In February 1849 Colonel Sabine wished to know the difference of effect 
(under such circumstances as those in which the Toronto horizontal force 
magnetometer finds itself in magnetic storms, &c.) between a s/it in a shield 
and an index. ‘The slit had also occurred to Dr. Lloyd and others, and I 
resolved upon attempting a strictly practical solution of the question. 
But before the experiment had been tried upon paper, it struck me 
that the Daguerreotype process would be far preferable to Talbotype in 
these cases of rapid and great variations, if not in every case, in consequence 
of the greater sensitiveness, greater capability of retaining the integrity of its 
normal condition, and greater delicacy (or sharpness) of outline; and the 
result of the first trials fully confirmed the Colonel’s sagacious anticipations 
of the superiority of the slit, at the same time that the use of silver sur- 
faces became at once indispensable for future operations. On the 23rd of 
February, two specimens, extremely well defined, were procured, one in 
twenty seconds, the other in thirty, The first was the stronger (too strong). 
The next problem was to copy these impressions, for it was deemed too 
expensive and cumbersome to preserve them; and I spent much time in 
trials on Mr. Edwards’ plan, viz. that of pressing off a part of the mercury — 
upon black paper coated by a solution of isinglass. The sticking, and con-— 
sequent tearing of the long piece of paper presented great obstacles (amongst 
others) to the success of these attempts; and I began, with Mr. Malone’s 
obliging assistance, to try whether the Talbotype process could be applied 
profitably to copy these metalline impressions. A specimen is preserved; 
but we arrived at the conclusion that the trouble and cost of dime, &c.in the 
execution would be too great, and that no copy on paper could ever be so 
sharp and beautiful as the metalline impression itself. 
In the beginning of April I made a little experimental addition to the 
. 
82 REPORT—1849., 
~~ 
