1846.] 



THE CIVIL ENGINEEER AND ARCHITECT'S JOURNAL. 



303 



stance, and their power of absorbing or extinguishing a portion of that 

 light during that penetration. This had been experimentally decided by 

 thin plates of gold, through all the various shades of that melal, down to 

 the red of copper. Whether the title of the paper, however, exactly agreed 

 with the observed tacts or not, all must admit that tliese facts were most 

 important, and deserving of serious attention. He was not acquainted 

 with the substance — chrysainmate of potash — but its properties, both op- 

 tical and mechanical, seemed to be interesting. The plasticity which it 

 seemed to exhibit in particular occurred to him as curious ; and this re- 

 minded him of a somewhat analogous property lately discovered in the 

 substance plumbago, or the black lead which pencils are made of. It is 

 w ell known lluit that substance can only be obtained in any purity at Bor- 

 rowdale, in Cumberland, and is lately becoming very scarce. Now, al- 

 though the powder of plumbago is one of tile best materials for preveutiog 

 friction, or the partial adhesion of other things, yet it has been lately found 

 that the particles of the powder themselves are capable of being made to 

 adhere i[]to a mass — indeed, more compact and uniform in its texture than 

 the best mineral plumbago, by simply inclosing it in a case, extracting the 

 air from among the particles, and subjecting the mass to violent com- 

 pression. 



Professor Powell said that the young gentleman who sat near him was 

 the discoverer of the chrysammic acid, and would, perliaps, be kind enouah 

 to describe its mode of production. Mr. ScH^I^CK (of Kochdale) said that 

 he had discovered the acid, which was part of the composition of the salt 

 of which Sir D. Brewster's paper treated. It was formed by the action of 

 boiling nitric acid upon aloes, and was one of the last products of that 

 action. The chrysammate of potash was a beautiful and curious salt ; and 

 although so plastic as to be readily moulded into thin plates, was yet so 

 si)aringly soluble as to require above 1,500 times its weight of water to 

 dissolve it. 



" On Elliptic Polarization." By Mr. Dale. 



" On certain Cases of Elliptic Polarization of LiglU by Reflection." By 

 Prefessor Powell. 



" On some of the Results of the Magnetic Uhsercalions made at General 

 Sir T. M. Brisbane's Observatory, Makerstoun." By J. A. Broun. — 

 1st. Magnetic Declination. — The annual diminution of westerly declina- 

 tion at iMakerstoun is 5' 8". M'hen proportional parts of this have been 

 added to the monthly means, from January 1814, till August 184fi, their 

 whole range is only 2' 1" ; that is to say, the mean position of tlie magnetic 

 needle fur any month, freed from secular change, has not been about 2' 1" 

 farther west than the mean position for auy other month. Mr. Broun 

 conceives that he has found the annual period of westerly declination to 

 consist of a minimum at the vernal, and of a maximum at the autumnal, 

 equinox : the mean range being under 1' 2". From the observations for 

 1843, Mr. Broun has concluded that there is a maximum of westerly de- 

 clination when the sun and moon are in opposition, and a minimum when 

 they arc in conjunction ; that there is a maximum of westerly declination 

 when the moon has its greatest north, and also when it has its greatest 

 south declination, minima occurring when it crosses the equator, in the 

 diurnal jieriod, the double maximum and minimum have been found 

 to exist in each month of the year. In the " Transactions of the Royal 

 Society of Edinburgh," Mr. Broua'has given certain results relating to the 

 horizontal and vertical components of the earth's magnetic force; but these 

 results were obtained in scale divisions corrected tor temperature by his 

 metliod. In order to deduce the variations of magnetic dip and of the 

 total magnetic force, from the variations of these components, it was neces- 

 sary to determine the values of the scale divisions in known units. Jlr. 

 Broun had previously shown* the inapplicability of the method given by 

 the Committee of Physics of the Koyal Society of London for the balance 

 magnetometer. He now described a metliud by which the \a!ue of the 

 micrometer divisions may be satisfactorily determined. This metliod will 

 be found in the Introduction lo the Makerstoun Observations for 1S43. 

 He has applied the same method lo the biSlar magnetometer, and has 

 found that the value of the scale divisions, obtained in the way recoiu- 

 inended by the Committee of Physics, is also inaccurate for this instru- 

 ment. With the aid of the values obtained by the new method, the follow- 

 ing results have been deduced 2ad. Magnetic Di/i.—Tlte dip is a niini- 

 inuin when the sun and moon are in opposition. In the mean diurnal 

 period for the year, 



Ttie priDcipal miiximum occurs at lOli. lum. a.m. 

 „ miiiimutn ,, o 40 p.ui. 



A secondary maximum „ 2 a.m. 



., minimum „ -S 40 p.m. 



iMakerstoun mean time being always used. These periods vary to some 

 extent throughout ihe year, the principal minimum occurring at G a.m. in 

 winter; the two minima being nearly equal to the cquitioses, and the 

 diurnal curve being smgle in summer. Mr. Broun has found that there is 

 a maximum of dip about four hours and a half before the iikkjo's passage 

 of the superior meridian; a inininiiiin about half an hour after the passage; 

 a secondary minimum about three hours after it ; and a secundary max- 

 imum about eight hours after it. 3rd. Total Force of the Earth's Mag- 

 netism. — A minimum occurs s\bi n the sun and moon are in opposition, 

 equal maxima near the quadratures, and a secoudary minimum at the time 

 lit conjunction. In the mean diurnal period for the year, 



* Trans. Roy. Soc. Edin. vol. xvi. 



The principal maximum occurs at 5ti. 40m. p.m. 

 „ minimum „ 2 10 a.m. 



A secondary maximum „ 7 10 a.m. 



„ minimum „ 10 10 a.ni. 



The periods of maxima and minima shift about two hours in the course of 

 the year, and in summer the principal minimum occurs at lOh. 30m. a.m. 

 The variations of force with reference to the moon's hour angle were found 

 by Mr. Broun as follows: — The principal maximum occurs about two 

 hours after the moon's passage of Ihe inferior meridian ; a secondary mini- 

 muni about fiiur hours before the passage of the superior meridian; a se- 

 condary maximum about one hour after the superior passage; and the 

 principal minimum about six hours and a half after that passage. Curves 

 were exhibited illustrating these results, and also the diurnal motion of a 

 magnetic needle freely suspended in the direction of the magnetic force. 

 From the latter some curious results have been deduced, which will be 

 found elsewhere. It will be enough to mention, at present, that in the 

 mean for the year, the motion from 6 a.m. till 6 p.m. is very trilling ; be- 

 tween midnight and 6 a.m. the needle is almost stationary, nearly the 

 whole motion occurring between G a.m., noon, and G p.m. The end of the 

 needle describes an ellipse whose major axis is at right angles to the 

 magnetic meridian ; but the direction of this axis varies throughout the 

 year. 



Blr. Hopkins, " On the relations of the Semi.Diurnal Movements »/ the 

 Barometer to Land and Sea Breezes." — Mr. Hopkins exhibited diagrams, 

 drawn up from Col. Sabine's paper " On the Meteorology of Bombay," of 

 the diurnal temperature curve, total pressure curve, and gaseous pressure 

 curve; with a diagram representing the swelling and sinking of the land 

 and sea breezes ; and endeavoured to show that these were inconsistent 

 with the explanation given by Col. Sabine, but harmonised with alterna- 

 tions of pressure caused by the alternate extrication of heat and absorptioa 

 of it during the alternate evaporations and depositions of water, in the 

 state of clouds and dew. 



Capl. Shortrede asked Mr. Hopkins several questions ; and, from his 

 own observations in India, extending over many years, must dissent from 

 Mr. Hopkins, as to the manner in which he supposed clouds to form and 

 disperse. The effects he ascribed were disproved by the fact, that several 

 miles inland, when there were no land and sea breezes, the clouds were 

 formed and dispersed in precisely the same manner. 



Section B.— Chemistry and Mineralogy. 



President: Mr. Faraday. — Vice-Presidetits: Prof. GJrove, Dr. Andrews, 

 Prof. Johnston, Dr. Daubeny. — Secretaries : Dr. Miller, Messrs. R. 

 Hunt, M'. Randall. — Committee: Prof. Rose, M. Dumas, Prof. Oer- 

 sted, Dr. Playfair, Prof. Solly, Mr. J. Prideaux, Prof. Schcjnbein, Prof. 

 Forchhammer, Messrs. R. Mallett, H. Osborn, W. West, R. WarringtoD 

 Dr. Leesou, Messrs. J . Wilson, \V. Lucas, T. J. Pearsall, T. AVard,' 

 Capt. Ibbetson, Dr. Percy, aiessrs. W. Sharpe, T. P. Gassiot, Prof* 

 Counel, Mr. J. P. Joule, Dr. Schunk, Messrs. T. Henry, W. Francis* 

 Rev. J. Barlow, Dr. Letheby, Messrs. P. Johnson, — Maskelyo. 



" On the Pirserice of Atmospheric Air and Uncombined Chlorine and 

 Carbonic Acid found in the Water of some of the Wells in the Suburbs of 

 Southampton, and their Action on Lead." By H. Osborn. — The principal 

 object of this paper was lo caution persons residing in the neighbourhood 

 of Souihauiptoii, against the use of leaden pipes for conveying water, and 

 to induce them to avoid the use of lead in auy form lor that purpose, with- 

 out having the water previously examined in order lo ascertain whether it 

 possessed the property of acting upon the melal and holding it in solution. 

 The author brought forward several instances of the serious cousequences 

 which had resulted from the use of water impiegnated with lead, and 

 pointed out the ditlerent solvent principles found in the water; one of 

 which was uncombined chlorine discovered in a spring in the New Forest. 

 The water possessed the property of bleaching brazil paper, and reddening 

 litmus paper by evaporation. The amount of uncombined chlorine was 

 estimated as cliloride of silver, — by deducting the amouut of the latter 

 contained in 20 ounces of water from that of the chlorine contained in the 

 solid contenls, the former weighing 1'2 more than the latter — thus indicat- 

 ing 0'296 of uncombined cjhloriue, which is capable of uniting with 0-864 

 of lead, forming I'lG of chloride of lead in the imperial pint. The lead 

 held in solution by carbouic acid, and the oxygen of atmospheric air, was 

 converted into chromate of lead, and estimated as chloride of lead; which 

 indicated 0*2.j or 0'2 of the oxide in twenty ounces of water. I'he solid 

 contents in an imperial pint were found to vary from one grain to three 

 grains, and to be composed of Ihe chlorides of sodium, calcium, and mag- 

 nesium, sulphate of lime, silica, and vegetable matter. Notwithstanding 

 the preservative property, which the salts contained in spring water are 

 said to possess, by forming an insoluble crust in the interior of the pipes, 

 it was found that the leaden pipes had been in use foj some years, and the 

 action of the water on the lead still continued with as much energy as 

 when they were tirst laid down, thus showing the presence of the above 

 solvents, and that they met with no resistance from the presence of the 

 saline matter. 



Dr. Dai Biisv made some remarks pointing out the importance of the 

 inquiry of Mr. Osborn, and the necessity of paying attention to the condi- 

 tion of the water supplied to towns through leaden pipes, or received in 

 leaden cisterns. — Mr. Pearsall stated that he found that the presence of 

 lead may be constantly removed from the water by the action of carbon, 

 and that lead may be always separated by well agitating the water in conj 



3J* 



