;S6 



NA TURE 



[April 23, 1903 



been overlooked. More elaborate hypotheses may be 

 needed, but not until the simpler have been disproved. 



Grantchester, Cambridge, April 10. W. Bateson. 



P.S. — A reviewer declares (Nature, April 9) that the data 

 in this case are " by no means easy of interpretation," on 

 what hypothesis 1 know not; and that "much of the 

 evidence is prima facie in favour of ancestral inheritance." 

 ll is scarcely too much to state that in each set of matings 

 the distribution (1) of pink and dark-eyed, (2) of coloured 

 and albino coats, (3) of " waltzers " and non-waltzers. is 

 in punctilious agreement with Mendelian prediction. The 

 variety of colour in the first cross I have dealt with. Know- 

 ing something of the recent history of fancy mice, two kinds 

 of grey in this generation cause me no surprise. In the 

 whole evidence 1 can find only three real difficulties, all 

 surely of minor importance. One is named in my letter. 

 I he second is the occurrence of three dark-eyed fawn- 

 yellows in the offspring of first crosses. The third is 

 the scarcity of yellows in the offspring of hybrids X albinos. 

 If the individuality of the parents were declared, two, 

 perhaps all, of these points could be cleared up. I am not 

 acauainted with any other conception of heredity which 

 elucidates any part of the facts. 



Experiment to Illustrate Precession and Nutation. 

 The following account of a simple experiment may be of 

 interest to some of the readers of Nature. The common 

 peg-top and tee-tolum are commonly referred to as affording 

 a good example of the phenomenon of precession. I do not 

 think that it is generally known that the motion of nutation 

 can be beautifully shown by the same simple means. Sir 

 John Herschel says in his "Outlines of Astronomy " that 

 the motion of precession can be shown by " that amusing 

 toy, the te-to-tum, which, when delicately executed and 

 nicely balanced, becomes an elegant philosophical instru- 

 ment." If, however, tin- tee- 

 totum is not perfectly balanced 

 we have realised the conditions 

 for showing nutation also. 

 If the earth were perfectly 

 homogeneous and undisturbed 

 by any outside irregularity, 

 there would be no nutation. 

 In the same way a tee-totum 

 will not exhibit the motion 

 of nutation if it be perfectly 

 balanced. When, however, 

 one side is made heavier than 

 the other we obtain the 

 phenomenon of nutation. The 

 magnitude of the nutation 

 increases with the extra 

 weight. A series of experi- 

 ments was made by spinning 

 a small clock wheel on its axis. The best way to see the 

 result is to spin the wheel on a white plate which has been 

 smoked. The trace thus obtained may be studied perfectly. 

 In order to get a permanent record, the wheel was made 

 10 spin cm a piece of char glass which had been slightly 

 smoked. The record thus obtained may be used as an 

 ordinary negative, and prints obtained on sensitive paper 

 in the ordinary way. With a little care very beautiful and 

 instinctive results may be obtained. The little apparatus 

 may also be projected on the screen, and the actual form- 

 ation of the curve exhibited. H. Y. Gill. 

 ( fecngoweswood College, Sallins, Co. Kildare. 



Fig. 1 — Trace made by imperfectly 

 balanced watch wheel spinning 

 on its axis, illustrating pre- 

 1 vision and nutation. 



Distribution of Ptthophora. 

 Is October last, I found an. old-established paddy-field near 

 Tanabe, the bottom of which, to the extent of several tens of 

 feel every way, was luxuriantly grown with the Pithophora 

 Oedogonia, Wittrock, var. Vaucherioides, Wolle, with rest- 

 ing spores yet incompletely formed. The locality is some 

 sixty miles south of Wakayama Shi, where I had gathered 

 the same with full spores, October, 1901 (see Nature, vol. 

 lxvi, pp. 270, 296). The occurrences of the alga in such 

 distant places seem to prove that it is indigenous to Japan. 

 The Floridan specimens I collected in 1891-92 were with 

 - 1 >• res mature in the months of June and July. 



KUMAGUSU MlNAKATA. 



Mount Nachi, Kii, Japan, March 10. 

 NO. 1747, VOL. 67] 



PEDIGREES. 

 PHE trouble of compiling pedigrees and their un- 

 *■ manageable size led me to devise a method of 

 recording relationships in a form suitable to my own 

 particular wants. As it promises to answer exceed- 

 ingly well, and to be of more extended utility, I 

 venture to publish it. 



The system of relationships between those who live 

 or have lived in a long-established community is wide 

 in extent, of indefinite depth, and interlaced in all 

 directions. The problem is how to arrange its records 

 so that when any individual is selected as a point of 

 departure, it shall be easy to trace his relationships in 

 every direction, whether ascending, descending, or 

 collateral, so far as materials exist. The represent- 

 ation of such a system is wholly beyond the powers 

 of a chart, but its object can be attained by breaking 

 it up into what will be called " Family Groups," each 

 of which slightly overlaps those with which it is imme- 

 diately connected. A family group, in the sense used 

 here, consists of (1) a parental couple, (2) all their sons 

 and daughters, (3) the wives and husbands of them. 

 Their names are supposed to be written on one page 

 ol a register, and the group, as a whole, to be defined 

 by the No. of that page. The group is also defined 

 and indexed under the joined surnames of the parental 

 couple. I subjoin three specimen groups, but in a 

 much abbreviated form for the sake of compactness, 



Family Groups. 



only half a line being allotted to each individual. In 

 reality, a short paragraph of full-length lines would 

 be used, to admit of the entry of long names, and of 

 such details as are commonly inserted in pedigrees. 

 Taking group 205 as our subject for explanation, 

 it will be observed that each of the five members of 

 the fraternity — Frank, Amy, Anne, Alex, and Rose 

 — bear the same register No. of 205, which defines 

 that group. The justification for indexing them in 

 the same group lies in the solidarity of each fraternity, 



