VOI~ LX.] PHILOSOPHICAL TRANSACTIONS. 68 



of 1.95, which I find by my experiments; the same calculus would give 2.24 

 lin. for the excess of the Ponoi pendulum, instead of 2.15 lin. which results 

 from my experiments. Hence it would follow tliat the increments of gravity 

 follow a ratio somewhat greater than that of the squares of the sines of 

 latitudes; and this result is confirmed by the experiments made at Pello in 

 Lapland, by the French academicians. 



4". I observed several times very exactly at Ponoi, the declination of the mag- 

 netic needle l" 10' east. 



5°. Exact observations of the inclination of the needle made in different 

 places of our globe, combined with those made long ago on the declination, 

 would be very interesting and projier for the advancement of our knowledge, 

 as to the theory of magnetism, which hitherto is but little understood. It is the 

 difficulty of making such observations, and obtaining accurate results, which 

 hitherto is but little understood. It is the difficulty of making such observa- 

 tions, and obtaining accurate results, which has discouraged philosophers and 

 travellers; but it is surprizing that so little has been done in this matter, since 

 Dr. Daniel Bernoulli furnished us with new ideas for constructing a machine fit 

 for determining the true magnetic inclination, in a memoir, which gained the 

 prize proposed for this subject by the Paris Academy, in 1743. He got an 

 inclinatory needle constructed at Basle, on new principles, and the experiments 

 he made assured him of success; he found the inclination at Basle 7li- degrees. 



Mr. Euler, the son, made use of the same compass at Berlin, but by 

 employing a method entirely different from that of Dr. Bernoulli. He gives 

 the particulars in the Memoirs of the Academy of Berlin, 1755. After a great 

 number of observations, he found the inclination to be then at Berlin between 

 724- and 73 degrees. At Petersburg I got constructed a like machine, and used 

 it for determining the inclination at Petersburg, Kola, and Ponoi ; I employed 

 both the methods of Messrs. Bernoulli and Euler, and found a wonderful 

 agreement in the results drawn from a great number of experiments. Two 

 needles made by different artists, one at Basle, the other at Petersburg, con- 

 sequently susceptible of a different magnetic force, produced but very minute 

 differences, inevitable in such delicate experiments; the several particulars are 

 recited in the papers I have sent to the Petersburg Academy, whence it may be 

 concluded that it is possible to determine with this instrument the true inclination 

 of the magnetic needle, without being any way liable to an error of half a degree 

 in the result, which in my experiments is as follows: viz. in 1769, the 

 inclination. 



At Petersburg, lat. 59° 55', long. 48°, was 73°^ 



At Ponoi lat. 67 4, long. 58° 51' 76 4. 



At Kola lat. 68 54, long. 49 45 77 ^ 



