On the Contraction of JVater ly Heat. 153 



the proportion between the equatorial and polar diameters 

 determined in the year 17S9*; and found that, in order to 

 be a perfect resemblance, my figure required some small 

 reduction of the longest diameter, so as to bring it nearly 

 to agree with the measures taken the 27th of May. When 

 I had made the necessary alteration, my artificial Saturn 

 was again compared with the telescopic representation of the 

 planet, and I was then satisfied that it had all the correct- 

 ness of which a judgment of the eye is capable. An exact 

 copy of it is given in Plate VII. The dimensions of it in 

 proportional parts are, 



The diameter of the greatest curvature - 3f> 

 The equatorial diameter - - 33 



The polar diameter - - - 32 



Latitude of the longest diameter - 43" 20' 



The foregoing observations of the figure of the body of 

 Saturn, will lead to some intricate researches, by which the 

 quantity of matter in the ring, and its solidity, may be in 

 some rneasure ascertained. They also afford a new instance 

 of the effect of gravitation on the figure of planets ; for in 

 the case of Saturn, we shall have to consider the opposite 

 influence of two centripetal and two centrifugal forces : the 

 rotation of both the ring and planet having been ascertained 

 in some of my former papers. 



XXXV. Experiments and Olservaiiovs vpon the Contrac- 

 tion of JVatcr bij Heat at low Temperatures, i?// Thomas 

 Charles Hope, M.D. F.R.S. Edin., Professor of 

 Chemistiij in the University of Edinburgh*. 



J. o the general law, that bodies are expanded by heat, and 

 contracted by cold, water at the point of congelation, and 

 for some degrees of temperature above it, seems to afford a 

 very singular and curious exception. 



The cncumstances of this remarkable anomaly have been 

 for some time believed to be the followmg : 



When heat is applied to water ice-cold, or at a tempera- 

 ture not far distant, it causes a diminution in the bulk of 

 the fluid. The water contracts, and continues to contract, 

 with the augmentation of temperature, till it reaches the 



• See Phil. Trans for 17!>0, p. 17. 



+ From tlic Tramacliom of the Royal Svcicty nf EdMurgh, part ii. of 

 vol. V. 



40th 



