TRANSACTIONS OF THK SJiCTlONS. 41 



tative stage ; and the author communicated the results of experiments (can-ied out 

 in his laboratory by Mr. A. McDougall, B.Sc.) instituted for the purpose of estab- 

 lishing facts upon which a quantitative photography might be foimded, the method 

 being based upon the expeiimental law, discovered by Professor Bunsen and himself, 

 to the eflect that a constant product of the intensities of the acting light into the 

 times of exposure always corresponded to a constant tint on the photogi-aphic paper. 

 Hence, if several differently sensitive prepared papers are exposed to a constant 

 light for varying periods of time, until they all exhibit the same degree of tint, the 

 reciprocals of these times of exposure represent the relative sensitiveness of the 

 papers. By the help of the pendulum-photometer, the times during which the 

 papers had been exposed were ascertained, and the degree of tint attained was read 

 off by the soda light. Tables were consti-ucted showing the variation in the sensi- 

 tiveness produced by increasing the strength of the solution of salts emploj'ed, and 

 curves drawn representing this relation. The salts used were chloride of sodium, 

 chloride of potassium, chloride of ammonium, and bromide of potassium. The 

 next point ascertained was the fact that the sensitiveness of the paper did not vary 

 with vaiiation of the base with which the chlorine or bromine was combined. The 

 third portion of the experiments referred to the comparison of the relative sensi- 

 tiveness of the chloride, bromide, and iodide, and mixtures of these. 



Description of a Chemical Photometer for Meteorological Ohservation, 

 By Professor Roscoe, B.A., Ph.D., F.E.S., F.C.S. 



The author exhibited and described a modification of the pendulum chemical 

 photometer, by means of which the meteorological registi-ation of the chemical 

 action of light may be accm-ately and easily earned on. No less than forty curves 

 of the daily chemical intensity at Manchester, in the year 1863-64, have thus been 

 made. The author believes that the method is now so simple that such a series of 

 determinations may be carried on at any meteorological observator}'. 



Note on the Existence of Lithium, Strontium, and Copper in the Bath Waters, 

 By Professor Eoscoe, B.A., Ph.D., F.E.S. , F.C.S. 

 At the request of Sir Charles Lyell, the author imdertook the examination of the 

 residue obtained by the evaporation of the Bath waters (King's Bath spring) by 

 spectrum-analysis. No trace of barium was foimd ; but strontium was present in 

 quantities sufficientlj' large to enable it to be easily detected. The portion of the 

 deposit soluble in dilute hydrochloric acid was freed from alkaline earths by several 

 precipitations with carbonate and oxalate of ammonia, and in this precipitate 

 strontium was again detected. The magnesiimi was next separated by ignition of 

 the mixed chlorides with oxide of mercury ; and, on examining the portions of the 

 residue soluble in water, the red lithium line was plainly visible. In salts derived 

 from twenty gallons of water the author was stiU unable to detect the smallest 

 traces of either rubidium or cfesium. In the course of both analyses the presence 

 of copper was detected. 



On some probable New Sources of Thallium. By "W. L. Scott. 

 Some time back, during the examination of a fine but highly ferruginous sand, 

 obtained from the neighbourhood of "Whitby, it struck the author as remarkable 

 that a certain precipitate, which he knew to be entirely free from both barium and 

 copper, should tint a hydrogen flame green. On going into the matter somewhat 

 more carefuUy, he found that this precipitate exhibited the thallic spectrum very 

 distinctly'. From this he was led to examine other sands; amongst them, those 

 from Alum Bay, Isle of Wight, and some others. The sands containing the thal- 

 lium are the rock-sands; the sea-shore sand, as a rule, contains no thallium. 

 Many of the deeply colom-ed clays which alternate with the sands at ^\^lum Bay 

 also give indications, more or less marked, of containing thallium. 



On Coppcr-smeltiny. By P. Spence, i^.C./S'. 

 The author said he had for some years directed his attention to this subject, and 



