300 Description of a Mercurial Log- Glass. 



mark on the log slate, in a column which should he traced upon 

 the slate for the purpose. 



In my own practice I have always caused two columns to be 

 marked, the one T. A. for temperature of the air, the other 

 T. W. for temperature of the water. In these columns I or- 

 dered t|ie officer of the watch to insert the temperature both of 

 the air and water twice (sometimes oftener) each \vatch. The 

 temperature of the air is, however, of little importance further 

 than as a comparative observation, it being only the variations 

 of temperature in the water which are of importance to the na- 

 vigator. 



In reading off, the observer should take care to keep as much 

 of the thermometer as possible immersed in the water, which 

 this marine case allows of being done with facility. 



I have said enough to convince vou of the immense imjiort- 

 ance of the thermometer as a nautical instrument, and that Mr. 

 Jamieson's Marine Case renders the use of it both more easy 

 and certain. I am, Sir, Andrew Livingston, 



IVilliam Warren, Esq. Shipmaster. 



P. S. You are at perfect liberty to use this letter in any mode 

 you think may be advantageous to Mr. Jamieson, whom I con- 

 sider entitled to much credit for this simple and useful invention. 



A.L. 



2nd P. S. Since writing the above, Mr. Jamieson has informed 

 me that he is anxious to send the instrument with which the ex- 

 periments were actually made at Greenock, and begged me to let 

 him have it, promising to replace it to me. Although with some 

 reluctance, I have complied. Thus theSociety of Arts will actually 

 have the real marine thermometer case in place of a model ; and I 

 doubt not but the scientific members of that honourable body, will 

 neither wish its size or weight increased, whatever individuals 

 (here) ignorant of seamanship may say. A. L. 



XLTX. Description of a Mercurial Log-Glass, invented by 

 Mr. C. II. Jhytiisos, nj' Carburton-slreet, Fitzroy-sqiiarc'^ . 



12b, Carbui ton-street, Fitzroy-squarc, April 4, 1820. 

 , HAVE the honour to send for the inspection and appro- 

 bation of the Society, a Log-glass invented by me: it is intended to 

 correct the errors constantly attending those at present used ; the 

 particles of sand with which they are generally filled being lial)le 

 to cohere, particularly in damp weather, and thus to impede and 

 even stop the performance of the instrument. 



• From tlie TraihSfniionx iif the Soacdj for (he Eiicnnroi^exicnt of Arts, 

 Manufiiclurc.i, and Commerce, for ISl'U. Tlie tjocitly's larj;e Silver Medal 

 was voted fur this eummuniidlioiu 



The 



