I860.] Physics. 323 



a globule of mercury, which serves as an indicator. As long as the 

 spirit rises, this globule remains stationary ; but as soon as the spirit 

 descends, the mercury sinks likewise, lengthening into a small cylin- 

 der, about l-10th or l-12th of an inch long, which cuts in two the 

 column of alcohol. It is evident that on adding to the degrees 

 marked by the extremity of the spirit-column, those shown by the 

 inferior extremity of the indicator on the lower scale, we ascertained 

 at once the maximum of heat to which tbe apparatus has been ex- 

 posed. Upon warming the bulb of the instrument with the hand till 

 the mercury reaches the enlargement, and then placing the instrument 

 flat while the spirit cools, the thermometer is ready for another obser- 

 vation. The advantages of an instrument of this kind are — 1, it is 

 available for taking observations where only an upright thermometer 

 can be used ; 2, it is not affected by travelling ; and 3, it is very easy 

 to make. 



The use of petroleum as steam fuel in place of coal, is attracting 

 considerable attention. Mr. C. J. Richardson is conducting experi- 

 ments at Woolwich Dockyard, with the view to test the capability of 

 petroleum to supersede coal and other fuel on board ship. Dr. Paul 

 has published some calculations, in which he attempts to prove that 

 the proposed application of it is based upon erroneous impressions 

 respecting the composition and character of petroleum as compared 

 with coal. He starts with the statement that the oil can be so utilized 

 that one ton is equal for steam purposes to five tons of coal. Now, 

 the specific gravity of coal being about 1 * 44, whilst that of petroleum 

 is from • 80 to • 85, the weight of a cubic foot of these materials 

 would be respectively — coal 901bs., and petroleum 501bs to 531bs. 

 But since petroleum, being liquid, lies in a more compact manner than 

 coal, in estimating the spaces occupied by these materials an allowance 

 of one-third should be made for the interstices or empty spaces 

 between the lumps of coal; so that the spaces occupied by equal 

 weights of coal and petroleum are about as 1 is to 1 • 2 or 1 • 4. Then 

 the relative heating-power of equal weights of coal and petroleum, 

 depending upon their respective chemical composition, are in the 

 following ratio : — Calorific power— coal, 1*02, petroleum, 1'50; and 

 the spaces occupied by quantities of petroleum and of coal would be 

 in the ratio of 1 to 1 • 16 ; a difference in favour of petroleum too 

 small to admit of any advantage being gained in regard to stowage. 

 The question of price, moreover, must not be left out in such discus- 

 sions. Dr. Paul argues that, since the price of petroleum varies from 

 15?. to 201. per ton, whilst that of coal used for steam- vessels varies 

 from under 1Z. to 31. 10s., the cost of equal quantities of heat produced 

 from these materials would be, under the most favourable circum- 

 stances, as in the ratio of 151. to 4Z. In addition to this, the highly 

 inflammable nature of petroleum must be considered. Its storage on 

 board a ship would require the use of air-tight vessels, and even then 

 there might be considerable risk of the production of explosive mix- 

 tures of the petroleum vapour and air. What, asks Dr. Paul, would 

 be the condition of a vessel of war provided with petroleum as fuel if 



