192 ANNUAL OF SCIENTIFIC DISCOVERY. 



evidently be destroyed if the areometer be filled with any liquid, but will be 

 restored if the areometer and the counter-balancing weight be plunged in 

 a liquid of the same specific gravity as that which it contains; and, as the 

 thin partition allows the liquid contained to expand in accordance with the 

 temperature to which it may be subjected, a very simple calculation will 

 show that the recstablishment of the equilibrium is independent of the tem- 

 perature. As, moreover, the metal of which the instrument is made, is very 

 thin, and a good conductor of heat, the equilibrium of temperature will soon 

 be established between the interior and exterior liquid. 



Now, to reproduce in any quantity a liquid of given specific gravity: fill 

 the areometer with the given liquid, and plunge it and the equilibriating 

 weight into the heavier of the liquids to be mixed, and add the other until 

 the equilibrium is restored. The liquids will be rigorously of the same 

 specific gravity. 



^ETHESIOMETER. 



Considerable interest has been excited by an instrument, which it is pro- 

 posed to call an rethcsiometer, exhibited at a recent meeting of the Harvcian 

 Society, London, by Dr. Sievcking. It is constructed for the purpose of 

 measuring the comparative sensibility of different parts of the surface, and 

 consists of a rod of bell-metal, graduated into inches and tenths of an inch, 

 upon which two movable points slide. The distance at which a person is 

 able to distinguish the points as two separate impressions is a test of the sen- 

 sibility of a given part. Thus, a person in health is able to recognize two 

 points at the tips of the fingers Avhieh are less than one-tenth of an inch 

 apart; in paralytic conditions this space would widen in proportions to the 

 amount of insensibility; and the instrument, by measuring this space, be- 

 comes a physical test of considerable accuracy of the existence and extent 

 of paralysis of sensation. Dr. Sieveking stated that the ordinary mode of 

 determining the amount of sensation in such cases, by pinching or pricking 

 the patient, did not afford sufficiently satisfactory results; but that he found 

 the instrument which he exhibited useful as an aid to the physical diagnosis 

 of some nervous affections, and determining by actual measurement the prog- 

 ress of the disease. Generally speaking, the purposes of diagnosis would 

 be met by comparing the two corresponding points of the two sides of the 

 body; but where an absolute standard of comparison was required, Webster's 

 table, showing the sensibility of different parts of the body, and given in 

 Miiller's Physiology, would afford this. Med. Times and Gaz. 



SOLAR ECLIPSE OF MARCH, 1858. 



M. Quetelet, at Brussels, carefully observed two compensating pendulums, 

 in comparison with a chronometer, during the eclipse. The object was to see 

 whether their vibrations were slower, as Professor Zantedeschi thought would 

 be the case. The two pendulums were arranged so as to vibrate, the one par- 

 allel, the other perpendicular to the meridian. The one parallel to the meri- 

 dian showed no change, but the other showed a loss of more than a second 

 and a quarter per hour, during the eclipse. The record of observations made 

 several times a day for several days, both before and after the eclipse, show 

 that this was no accidental coincidence; but many more observations will be 

 necessary to establish the connection of effect and cause between it and the 

 eclipse. 



