324 



SCIENCE. 



[Vol. XIX. No 488 



tations of structure and habit. The second is by the pro- 

 duction of new individuals to take the place of those that 

 have been overcome. Now, as dlEferent animals exhibit 

 varying degrees of ability to adjust themselves to their en- 

 vironment, so also their reproductive power may be small or 

 great. In estimating this reproductive power four factors, 

 as Herbert Spencer points out,^ are to be taken account of, 

 namely, (1) the age at which reproduction commences, (2) the 

 frequency with which broods are produced, (3) the number 

 contained in each brood, and (4) the length of time during 

 which the bringing forth of broods continues. 



Accordingly, for the special case of Physa heterostropha 

 we have the following results: — 



1. Age at which reproduction begins, 5 months. 



2. Frequency of broods, 1 in about 2^'^^ days. 



3. Number in each brood, 30 average. 



4. Reproductive period, 4 months, March to July. 



Some addition ought to be made to this actually observed 

 period, inasmuch as the snails had certainly already entered 

 upon it at the time of their capture, and, further, instead of 

 closing normally, it seems to have been violently interrupted. 

 Just how much the period of reproduction is to be extended I 

 have no means of determining, unless the fact that the young 

 snails of the first brood were observed reproducing themselves 

 in September warrants an extension of at least two months, 

 making it six months instead of four. 



Assuming, then, that the reproductive season extends from 

 March to September, and assuming, further, somewhat arbi- 

 trarily, that the snail lives but two years, we have, on the 

 basis of facts above mentioned, the following estimate of the 

 total number of the offspring of a single pair: — 



At close of first season 1.900 



950 pairs at close of second season 1,805,000 



Original pair at close of second season 1,9 lO 



Total number o£ offspring In two years 1,808,800 



W. L. POTEAT. 



Wake Forest College, N.C. 



NEBRASKA SUGAR SCHOOL. 



Professor Lloyd has just made the 6rst formal report of 

 the sugar school at the State university, Lincoln, Neb., of 

 which the following is a summary : The school opened on 

 Jan. 5 with an enrollment of twenty-five students. These 

 students were mostly members of other classes in the chemi- 

 cal department of the university; the only preparation re- 

 quired for entrance being a clear conception of the princi- 

 ples of elementary chemistry, such as may be obtained in 

 some of the high schools of Nebraska. 



The course consisted of two lectures a week, with five 

 hours of laboratory work. The lectures as given by Mr. 

 Lyon embraced the following subjects: 1. Chemistry of the 

 sugars; 2. technology of beet-sugar man ufacture; 3. culture 

 of the sugar beet. 



The lectures under the first head were designed to give the 

 students an idea of the position of sugars as a class in the 

 series of compounds of carbon, and their relation to others of 

 these compounds, together witli a knowledge of the proper- 

 ties and characteristics of each of the sugars. 



The cause and effects of fermentation upon sugar solutions 

 were carefully studied. Other important principles relating 

 to the manuf.icture of sugar, as the compounds of the sugars 

 with lime, melassigenic action, etc., were taken up in order 

 to prepare the student for the complete understanding of the 

 practical application of these principles in sugar factories. 



> Biology, Vol. II., p. 395. 



A discussion of the methods of the analysis used in the 

 laboratory was given from time to time throughout the 

 course. 



Under the second head of lectures, the various processes 

 that the beets, juice, and sugars undergo from the washers 

 to the granulator were studied in detail. Both the French 

 and German forms of machinery were described. As each 

 process was studied, the methods of the analysis of its prod- 

 ucts and by-products was referred to. The study of sugar- 

 house control was in this way presented to the student. 



During the latter part of the winter term. Professor 

 DeWitt B. Brace gave the class four valuable lectures 

 on the theory of light. His lectures included the following 

 subjects: 1. The wave theory of light; 2. polarization of 

 ■light; 3. rotation of the plane of polarization; 4. application 

 of these principles to the polariscope and to the diflferent 

 forms of saccharimeters. 



The lectures were finely illustrated by means of the ap- 

 paratus in possession of the physical laboratory. This 

 course in the physics of light was followed by lectures in 

 the chemical department on the use of the saccharimeter, 

 methods of setting prisms to obtain a clear field, adjustment 

 of the compensating wedges, methods for testing the accuracy 

 of instruments. 



The laboratory work of the course consisted in analyses of 

 the various products and by-products of the sugar factory. 

 The samples used were obtained from the Norfolk sugar fac- 

 tory during the last campaign. One of the students did 

 some advance work in the absorption of sucrose by bone 

 black and the volume of the lead precipitates. 



The spring term was devoted to a course of lectures on the 

 culture of the beet. This course embraced the following 

 topics : 



1. Origin and history of the beet. 



2. External characteristics of a good sugar beet, its roots 

 and foliage. 



3. Composition and structure of the root. 



4. Relation of the leaves to the root. 



5. Food of the plant. 



6. Relation of the plant to the atmosphere and to the soil. 



7. Conditions governing the growth of the plant, and 

 changes during vegetation. 



8. Fertilizers, preparation of the soil, planting, cjltivating, 

 thinning, etc. 



9. Production and impi'ovement of the seed. 



These lectures were supplemented by practical work at the 

 station farm, which may be continued throughout the sum- 

 mer at the option of the student. The course closed May 6. 



Encouraged by this prosperous beginning of the first beet- 

 sugar school in the United States, it is hoped that in the 

 coming year the work may be greatly extended. Several 

 students who have taken the course outlined are thoroughly 

 prepared to do polariscopic work in sugar factories. 



SECONDARY BATTERIES.' 



When a lead-peroxide cell is discharged, sulphate of lead 

 is the ultimate product on both plates, and when it is charged 

 again this lead sulphate is oxidated on one plate and re- 

 duced on the other. This fact was published in 1882 by Dr. 

 J. H. Gladstone and the late Mr. Tribe in Nature. Taken 

 by itself, however, it does not explain how it is that during 

 charge the potential difference of a cell will rise rapidly 

 from 2.1 volts to 2.13 volts, then slowly to 2.3 volts, and 



'' From Engineering of jyiay 20. 



