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TRANSACTIONS OF THE SECTIONS. 23 
been given in the Proceedings of the Royal Irish Academy. The present communi- 
cation contains the results of a series of observations made with two of these instru- 
ments, one of which was erected at Toomavara, in the county of Tipperary, and the 
other at Monk’s Eleigh, in Suffolk. The observations embrace a period of one year, 
and are illustrated with diagrams, which represent the results obtained at the two 
stations, for the whole year, for each quarter of the year, and for the individual months. 
The following Table gives the results for the entire year, expressed in inches. 
S. S.W. | W. | N.W. N. | N.E. E. S.E. | Total. 

SS: ah Pee eee ee ee, ee ee eee ee 
Toomavara ...|4°249 |12-696 | 8-150 | 2°640 |3°115 | 3-078 | 3-101 | 3:523 | 40-552 
Monk’s Eleigh| 2:674 | 2°756|4:371 | 2:392 | 2°776 | 2:027 | 3:092 | 1-708 | 21°796 

It appears from this Table, that while the total amount of rain which falls in Tip- 
perary is nearly double of that which falls in Suffolk, there islikewise a wide difference 
between the two stations as to the quantity which falls with different winds. In fact, 
nearly one-third of the whole amount of rain falls at the Irish station during the pre- 
valence of the south-westerly winds, while at the English station there is a much 
Nearer approach to equality in the amount of rain borne by different winds, This 
prevalence of rain with the south-westerly wind is distinctly marked in every season 
of the year at the Irish station; while at the English one each season is characterized 
by an excess of rain from a different point of the compass, producing a near approach 
to uniformity in the results of the entire year. It is to be observed, that these results 
are integral effects. A comparison of them with the times of continuance of the re- 
spective winds, gives the raininess (if it may be so called) of the several winds, 
Experiments to prove that all Bodies are in some degree Inelastic, and a pro- 
posed Law for estimating the Deficiency. By E. Hopcxinson, £.R.S. 
Mr. Hodgkinson said it was a principle generally acknowledged in the present day, 
and employed by those who have written on the subjectof elasticity, that when bodies are 
acted upon by forces tending toelongate or compress them in a small degree, the changes 
produced are in proportion to those forces, and that equal extension and compression 
are produced by equal forces. That this principle is true, so long as the change pro- 
duced in bodigs is very small, isnot doubted; and as regards extensions, it is the basis 
of the early investigations of James Bernouilli on the elastic curve; of Hooke, who 
was its author (‘Theory of Springs’), Mariotte, Leibnitz (‘ De Resistentia Solidorum,’ 
1684). It was adopted in the profound inquiries of Euler on the strength of columns, 
which were corroborated by Lagrange (Berlin Memoirs) ; and with respect both to 
extensions and compressions, it forms the basis of the calculations on the strength and 
elasticity of bodies in the principal theoretical and practical works on mechanics of the 
present day, as the ‘ Mécanique’ of Poisson, and the works of Whewell, &c., the prac- 
tical treatises of Navier, Poncelet, Tredgold, Barlow, Moseley, &c, He hoped, however, 
to convince the Section that this principle does not operate alone in the resistance of 
bodies subjected to tension, or to compression, or to both. He hoped, too, to show the 
law which the element, not considered by writers, nor generally known to exist, is sub« 
ject to. This elementisa defect of elasticity, or set, to which all bodies made to undergo 
a change of form, however small, seem to be liable. The defect here mentioned was 
known to exist only when the body had been strained with a considerable force, or 
such as to be equal to one-third or upwards of the breaking weight. But the experi- 
ments which he should adduce would show that the defect commences with the smallest 
changes of form, and is increased according to the square of the extension, or com- 
pression, or of the weight. Thus, if e represent the extension or compression which 
the strained body had undergone, and ae the force which would have produced that 
extension or compression if the body had been perfectly elastic, the real force neces- 
sary to produce this change, e, will be less than the former by a quantity, b e”, repre- 
senting the defect of elasticity. Hence the force required to produce a change, e, is 
