ON REGISTERING EARTHQUAKE SHOCKS IN SCOTLAND. 85 



of strips of rolled zinc, and close the stop-cock. The capacity of the appa- 

 ratus is such, that after being thus charged, the whole space left for the gas 

 to accumulate in is nearly equal to four pints, and the volume of hydrogen 

 extricated in ten minutes is in round numbers 3000 cubic inches at the press- 

 ure of one atmosphere, which give in this case a pressure of 22 atmospheres 

 in the gauge. 



The Section will now see, that by a greater or less opening of the stop- 

 cocks a very extensive range of heat is commanded, according to the quantity 

 of gas which I allow to pass, so that the platina vessels may be brought gra- 

 dually or instantly from a moderate temperature to the highest white heat 

 which they are capable of bearing ; and it will be observed that the whole 

 surface of the crucible is heated with great uniformity when revolving within 

 the helical burner. This very intense heat might be continued, with the 

 present charge and burner of six jets, for nearly twenty minutes, and may be 

 discontinued and resumed at pleasure ; for such is the accuracy of the fitting, 

 that no material loss of gas occurs in many hours when the stop-cocks are 

 closed. 



Higher charges may be safely employed than I have here used, and the 

 accumulation of the gas may be retarded or accelerated by varying the 

 strength and volume of the charge ; but this will suffice to show the use and 

 power of the instrument. The invention of new instruments is often the first 

 step to the discovery of new facts and laws, and therefore I have bestowed 

 both a good deal of attention, and also of expense beyond the liberal grant 

 made by the Association, on this instrument, in the hope of bringing within 

 the reach of chemists as full a command of high heats as of low, with such 

 ceconomy of time, trouble and cost as may make it practically available. 



The actual cost of the apparatus here exhibited is enhanced by some sup- 

 plementary parts, serviceable in the first construction and regulation of it, 

 but not essential probably to its practical use ; and if the gauge and separate 

 drying-chamber, which are of this character, be deducted, the instrument may 

 be constructed at a moderate price. 



The expense of the charge which I have now used is less than sixpence; 

 the trouble of charging and re-charging is less than that of lighting and re- 

 lighting a fire. The only part of these operations which requires time is the 

 cooling the mixture of the acid and water, a precaution advisable when a 

 strong charge is used, lest the heat thus generated, added to that produced by 

 the solution of the zinc, should occasion an inconvenient evolution of steam. 



With the aid of this instrument I have made various experiments on vitri- 

 faction, especially on that of phosphoric glasses, into the detail of which, as 

 they are still in progress, I will not at present enter. The Section will, how- 

 ever, see on the table various specimens of vitrified compounds, which tend to 

 illustrate some leading principles in the manufacture of glass, and with regard 

 to which I shall be happy to furnish the Section with any information that 

 may be desired. 



Report of the Committee for registering Earthquake Shocks in Scotland. 



The place where, as usual, these shocks have been most felt during the last 

 twelve months, is Comrie in Perthshire ; thirty-seven shocks have been felt 

 there during that time; but few were so violent as to produce any effects be- 

 yond the neighbourhood of that town. 



The following is a list of the shocks registered at Comrie by Mr. Macfar- 

 lane, post-master there, who takes charge of the instruments belonging to the 

 Association : — 



