January 12, 1906.] 



SCIENCE. 



73 



until the reaction was completed. The most 

 decided deflection of the instrument occurred 

 in those oases where the reagent was permitted 

 to act more vigorously about one electrode 

 than the other. 



To test as to the possibility of the phe- 

 nomenon being due to a difierence in concen- 

 tration at the electrodes, the cell was nearly 

 filled with water and a saturated solution of 

 NaCl was introduced into the water about 

 one of the electrodes. While a very slight 

 deflection of the needle was manifest, it was 

 not in any case comparable with the result 

 mentioned above, being not greater than one 

 scale division. 



Another possibility is, of course, a thermal 

 effect. To test this the cell was again filled 

 with water and concentrated H,SO, was in- 

 troduced about one of the electrodes. A slight 

 deflection was noted — in magnitude about the 

 same as in the last-mentioned case, one scale 

 division. 



In addition to the above evidence against a 

 possible thermo efi^ect might be mentioned the 

 fact that the magnitude of the current did not 

 appear to be a function of the heat of reaction. 



The above would seem to indicate that the 

 current is not due to a difference in concen- 

 trations at the electrodes or to a thermo-effect. 

 However, the data at present at hand would 

 scarcely justify a definite conclusion in this 

 respect. 



As to the ultimate cause of the current ob- 

 served I am not at the present writing pre- 

 pared to venture an opinion. I make this 

 communication in order that other investi- 

 gators may test the matter for themselves. 



Chas. a. Culvee. 



Randal Morgan Laboratory of Physics, 

 University of Pennsylvania, 

 October 18, 1905. 



PEAR-LEAP BLISTER-MITE (eRIOPHYES PIRI NAL.). 



As with many of our orchard pests, this is 

 an introduced species, and was undoubtedly 

 brought into the United States in importa- 

 tions of nursery stock. Since its introduction 

 it has, largely through the nursery trade, been 

 widely distributed in the pear-growing sec- 

 tions, where it is usually a familiar pest of 



this kind of fruit. Within the past few years 

 added interest has been shown towards this 

 species in this state because of its attacks 

 upon apple foliage. In 1902 the attention of 

 this station was directed to its work in two 

 widely separated orchards, but during the past 

 two years it has been very conspicuous in 

 many orchards in various parts of the state 

 where it promises to be an important pest of 

 this fruit. 



In the study of the habits and distribution 

 of Eriophyes piri in the state of New York, 

 two other European species have been found 

 upon pear and apple leaves. These have been 

 recorded by Dr. Nalepa by the names of 

 Epiirimerus piri and Phyllocoptes schlechten- 

 dali. The latter are distinguished from Erio- 

 phyes piri in that the abdominal rings on 

 venter are nearly twice as many as on dorsum. 

 Epitrimerus piri differs from P. schlecMendali 

 by having two longitudinal furrows on dorsum 

 of abdomen. The former is found upon apple 

 ' and pear leaves, while the latter has so far 

 been detected only on apple foliage. 



P. J. Parrott. 

 N. Y. Agricultural Experiment Station, 

 Geneva, N. Y. 



QUOTATIONS. 



THE METRIC SYSTEM. 



The American people have a world-wide 

 reputation for their ingenuity in devices to 

 save time and labor. It is an anomaly that 

 such a progressive people has failed to see the 

 enormous loss of tirne and labor incurred in 

 the retention of medieval and confusing 

 weights and measures. 



■ Three fourths of the enormous foreign trade 

 of the United States last year was with coun- 

 tries having the metric system — the system 

 now in use among four hundred and fifty 

 millions of people. Merchants import liquids 

 by the liter, textiles by the meter, foods and 

 drugs by the kilogram, and the innumerable 

 consigTLinents must be calculated into and sold 

 by different measures of volume and of length 

 and by avoirdupois weight and troy weight 

 and apothecaries' weight. In exporting com- 

 modities, on the other hand, quantities, weights 

 and measures must be laboriously converted 



