348 



SCIENCE 



[N. S. Vol. XXV. No. 635 



2,179, in the fall courses within the quadrangles, 

 and a considerable loss, from 562 to 247, in the 

 courses outside the quadrangles. Owing to the 

 increase in the summer session figures, however, 

 there is a gain in the grand total. The change of 

 courses given for teachers from the center of the 

 city to the quadrangles, which took effect this fall, 

 has lessened the number of students in such 

 courses, but increased the efficiency of the work. 



As for individual schools, there has been a gain 

 in the academic department, especially in men, in 

 law and in pedagogy, while there has been a slight 

 loss in medicine, divinity and the graduate schools. 

 As in the case of the University of Pennsylvania, 

 a number of students enrolled in courses for 

 teachers have been included in the Chicago figures 

 who would be excluded in the Columbia or Har- 

 vard figures, but the time for making more defi- 

 nite inquiries wag too short. 



The following errors should also be noted: 

 In the list of institutions mentioned on page 

 794, column two, line eleven, Stanford should 

 be inserted between Kansas and Indiana; and 

 in line fifteen Chicago should be omitted. On 

 page 796, column one, line eighteen, Chicago 

 should be inserted before Harvard. In the 

 table, the number of men in the academic 

 department of Princeton University should 

 be 758, instead of 755. On page 794, column 

 one, line twenty, insert, before Missouri, 

 'Syracuse (48.Y1%).' Eudolf Tombo, Jr. 



ALCOHOL FROM CACTI 



To THE Editor of Science: In a letter 

 entitled ' Alcohol from Cacti,' which appeared 

 in the Scientific American for December 15, 

 the author referring to the results obtained 

 with this plant by a California chemist, states 

 that " from five pounds of pulp he distilled, in 

 a crude way, more than a gallon of alcohol, 

 which was clear in color, and burned readily 

 with a bright, warm glow." 



At the time this article appeared we were 

 hesitating about publishing the enclosed press 

 bulletin for fear the theoretical estimates 

 therein given would exceed the amount which 

 it would be possible to obtain in practise. 



Cactus will not average over 10 per cent, 

 carbohydrates, and if, as is usually estimated, 

 this yields one half its weight of 95 per cent, 

 alcohol, it is not clear how it would be possible 

 to obtain one gallon of alcohol from less than 



140 pounds of this plant. If, however, the 

 chemist referred to above can distil one gal- 

 lon (seven pounds) from five pounds of cactus 

 pulp, it would be interesting to know what the 

 strength of his product is, and whether or not 

 it was done with the assistance of a magi- 

 cian's wand. 



E. F. Hare 



AgEICULTUBAL CoUiEGE, 



New Mexico 



THE parthenogenesis OF ENCYRTUS 



At the time that my recent note on * Poly- 

 embryony and Sex-determination ' was written 

 I had not seen Silvestri's latest commuidca- 

 tion. In a brief, preliminary paper' he pre- 

 sents the results of his studies on the early 

 stages of the development of Encyrtus and 

 among other details notes the fact that, as in 

 Litomastix, there is parthenogenetic develop- 

 ment, unfertilized eggs always producing 

 males, fertilized ones only females. The ma- 

 turation and early segmentation stages studied 

 are identical in the two types. 



Wm. a. Eiley 



SPECIAL ARTICLES 



POLARIZATION AND INTERFERENCE PHENOMENA 

 WITH WHITE LIGHT 



I HAVE usually found great difficulty in en- 

 deavoring to explain the color phenomena ob- 

 tained with white light in rotary polarization, 

 in the behavior of thin plates with or without 

 polarized light, and in interferences and 

 diffractions generally, to an elementary class. 

 The following diagram, therefore, which yields 

 a large amount of information, may be of in- 

 terest to the reader, although it contains noth- 

 ing essentially novel. Note the occurrence of 

 d/\ throughout. 



Rotary Polarization. — If we write the rota- 

 tion 6 of the plane of polarization due to a 

 thickness d of quartz cut perpendicularly to 

 the axis, 



e = ir(\—v'/v") ■ d/y, 



where v' and v" are the velocities of right- 

 handed and left-handed rays in the crystal 

 ^ Silvestri, F., 1906, ' Sviluppo dell Ageniaspis 

 (Encyrtus) fuscicollis (Dalm.) Thorns.,' Atti Ace. 

 Lined (5), XV., pp. 650-658. 



