56 ANNUAL OF SCIENTIFIC DISCOVERY. 



GROUP III. 



Ratio of axes of thermal ellipse 1 to 1-50. Mean ratio of deflection 1 to 9-5. 



Apricot. 

 Pistachio. 

 Siberian Acacia. 



1'ernanibuco red wood. 

 Japan red wood. 

 1'uerte-Cabeilo yellow wood 



GROUP IV. 



Ratio of the axes of the thermal ellipse 1 to 18. Mean ratio of deflection 1 to 14-0. 



Willow (two examples). 



Chestnut (three examples). 



Lime. 



Alder. 



Birch. 



Poplar (three examples). 



A?pen. 



Pine. 



Fir. 



Wey mouth fir. 



Magnolia. 



Iron wood. 



Tamarind. 



Palmassu. 



" Kistenholz." 



Caoba (Havana Cedar). 



Savanilla yellow wood. 



ON THE MEASUREMENT OF RUNNING WATER BY WEIR BOARDS. 



The following report on the above subject has been presented to the Brit- 

 ish Association by Prof. James Thompson, of Belfast, Ireland: The exper- 

 iments proposed to be comprehended in the investigations to which the 

 present interim report of progress relates, have for their object to determine 

 the suitableness of triangular (or Y-shaped) notches in vertical plates for the 

 gauging of running water, instead of the rectangular notches in ordinary 

 use. The ordinary rectangular notches, accurately experimented on as they 

 have been, at great cost and with high scientific skill in various countries, 

 with the view of determining the necessary formulas and coefficients for 

 their application in practice, are, for many purposes, suitable and conve- 

 nient. They are, however, but ill-adapted for the measurement of very 

 variable quantities of water, such as commonly occur to the engineer to be 

 gauged in rivers and streams. If the rectangular notch is to be made wide 

 enough to allow the water to pass in flood times, it must be so wide that for 

 long periods, in moderately dry weather, the water flows so shallow over its 

 crest, that its indications cannot be relied on. To remove in some degree 

 this objection, gauges for rivers or streams are sometimes formed, in the 

 best engineering practice, with a small rectangular notch cut down below 

 the general level of the crest of a large rectangular notch. If, now, instead 

 of one depression being made, for dry weather use, in a crest wide enough 

 for use in floods, we conceive of a large number of depressions, extending so 

 as to give to the crest the appearance of a set of steps or stairs, and if we 

 conceive the number of such steps to become infinitely great, we are led at 

 once to the conception of the triangular instead of the rectangular notch. 

 The principle of the triangular notch being thus arrived at, it becomes evi- 

 dent that there is no necessity for having one side of the notch vertical, and 

 the other slanting; but that, as may in many cases prove more convenient, 

 both sides may be slanting, and their slopes may be alike. It is then to be 

 observed that, by the use of the triangular notch, with proper formulas and 

 coefficients, derivable by due union of theory and experiments, quantities of 

 running water from the smallest to the greatest, may be accurately gauged 

 by their flow through the same notch. The reason of this is obvious from 

 considering that, in the triangular notch, when the quantity flowing is very 



