614 



flection ; proceed at once to the observation of vibration, 

 determining the coefficient of torsion at the end ; and, lastly, 

 make the preliminary arrangements (of detorsion, &c.), for 

 the determination of the DecHnation, deferring the observa- 

 tion itself until 1 p.m. If there be a second observer, he 

 should undertake the observation of Inclination, and such 

 sextant observations as may be required for the determination 

 of the Latitude, the Time, or the true Meridian. The obser- 

 vation of Inclination should be simultaneous with that of the 

 Horizontal Intensity ; the astronomical observations may be 

 made whenever most convenient. 



The Theodolite Magnetometer may likewise be employed 

 with advantage in a fixed observatory, especially in observa- 

 tions of the absolute Intensity ; and it is worthy of remark, 

 that if the differential instruments used in connexion with 

 it be small ones, the circle of this instrument may be em- 

 ployed in their adjustments, and their construction thus re- 

 duced to the simplest possible form. 



Mr. Wm. R. Wilde read a notice of the opening of some 

 TumuH, by Mr. Nugent, and the Rev. Dr. Todd (V. P.) 

 on the part of Mr. Nugent, presented a stone of a peculiar 

 form, found in one of the Tumuli described. 



The thanks of the Academy were given to Mr. Nugent, 

 for his communication and donation. 



Mr. R. Mallet presented the results of his analysis of a 

 porcelain clay, discovered some years ago by him, at Howth, 

 and since extensively brought into use for the manufacture 

 of crucibles. 



The clay is found upon the southern side of the penin- 

 sula of Howth, which consists principally of quartz rock ; 

 it exists in large concretionary masses, or highly irregular 

 beds, and appears to have reached its present position by 



