466 



NATURE 



IMarch 15, 1888 



Too many Decimal Places. 



A COMMUNICATION in NATURE of January 26 (p. 294) ends 

 with the sweeping suggestion "that, as a rule, only experiment- 

 alists are capable of judging the limits of accuracy of experiment, 

 and that they may be trusted to save themselves trouble where 

 trouble may be saved without sacrificing accuracy." 



On the contrary, is it not true that experimenters, as a class, 

 have shown a marked tendency to give unnecessary trouble, both 

 to themselves and to those who utilize their reults, by using too 

 many significant figures in their numerical work ? The strictures 

 of mathematicians have done much to check this tendency. 

 But can it yet be claimed that their habits need no critical 

 inspection in this respect ? Not being prepared to bring forward 

 statistics, I can only make this remark in the form of a query, 

 which applies to the general statement quoted, rather than to 

 the merits of the special discussion which gave rise to it. In 

 vol. Ixi. (1871) of the Journal of the Franklin Institute, Prof. 

 Pickering has shown by graphical methods how greatly Regnault's 

 coefficients may be simplified. J. Rayner Edmands. 



Harvard College Observatory. 



"The Teaching of Elementary Chemistry." 



In Nature of February 23 (p. 389), an anonymous corre- 

 spondent, signing himself " Z.," draws attention to what he 

 calls " a few highly misleading passages in the two books 

 reviewed under the above heading in Nature of January 19." 



In the name of the authors of these books, I challenge " Z." 

 to make good his statement that the passage which he quotes 

 from p. 65 of the "Elementary Chemistry," concerning the 

 reaction between sodium and water, is "highly misleading." 

 We assert that the sentence is not misleading. The second 

 statement quoted by "Z." is not quite correct: chlorine mon- 

 oxide is prepared by passing dry chlorine over yellow mercuric 

 oxide, which has been previously dried at 300°-400°, at the 

 ordinary temperature, not over heated mercuric oxide, as stated 

 on p. 116 of the " Elementary Chemistry." We thank " Z." for 

 the correction. But, inasmuch as the result of passing chlorine 

 over yellow mercuric oxide dried at about 100° is to evolve 

 oxygen without forming chlorine monoxide, the correction does 

 not affect the argument, and it may still be justly said that in 

 making chlorine monoxide "we carry out a reaction in which 

 oxygen is produced in presence of chlorine." The supposed 

 contradiction found by "Z." between the directions given in 

 the " Practical Chemistry " to the student who is burning a 

 weighed quantity of magnesium — not to remove the lid of the 

 crucible lest some of the magnesia should be " volatilized and 

 lost" — and the statement in the "Elementary Chemistry," that 

 "no compound of magnesium has been gasified," rests upon a 

 verbal quibble. Volatilized and gasified have not precisely the 

 same connotation. I confidently assert that no student is in danger 

 of being misled by either of the statements which "Z." has quoted. 



" Z." states that the results of an experiment on the reaction 

 between potash and iodine, described on p. 63 of the " Practical 

 Chemistry," contradict the sentence on p. 62 of the same book 

 concerning the similarities between the chemical properties of 

 chlorine, bromine, and iodine. I reply that "Z." has here 

 shown himself to be unacquainted with the methods of chemical 

 classification ; and also that he has taken the word similar to 

 mean the same as identical. 



If "Z." will bring forward proofs that the statements he has 

 quoted are "highly misleading," and will sign his name to tlie 

 letter in which he states these proofs, I am ready to argue each 

 point with him in detail. But, if " Z " continues to charge the 

 authors of the books he has deigned to notice with making mis- 

 leading statements, while he himself remains anonymous, 1 shall 

 decline to take any notice of his communications. 



Cambridge, February 29. M. M. Pattison Muir. 



The Gale of March 11. 



I BEG to inclose the readings of my standard Robinson's cup- 

 anemometer during the gale of March 11 : — 

 II-12 a.m., 64 miles. 

 12- I p.m., 67 ,, 



1- 2 „ 71 „ 



2- 3 „ 73 „ 



3- 4 ,, 63 ,, 



General direction, S.W. ; altitude, 600 feet above mean sea- 

 level. C. E. Peek. 

 Rousdon Observatory, Lyme Regis, March 13. 



THE DISPERSION OF SEEDS AND PLANTS. 



TN a recent number of Nature (vol. xxxv. p. 151) I 

 ■*• mentioned instances which had come under my 

 observation, in which birds had taken an active part in 

 the dispersion of seeds and plants. Since then 1 have 

 come across further notes bearing upon the subject 

 which -is one of considerable interest and importance, as 

 it throws a direct light upon some at least of the agencies 

 whereby plant life has been distributed over the surface 

 of the globe. Although birds, from their greater adapt- 

 ability to rapid and extensive locomotion, are more con- 

 cerned than any other animals in the dispersion of plants, 

 they are by no means alone in this work. 



It may seem strange, at first sight, to assert that cattle 

 have been the means of distributing the seeds of certain 

 plants from one country to another, but a statement is 

 made by Grisebach ^ respecting Pithecolobiiint Sanian 

 (N.O. Leguminosa:;), a large tree native of Tropical 

 America, now naturalized in Jamaica, that the "seeds 

 were formerly brought over from the continent [of 

 America] by cattle." This statement has been carefully 

 examined, and it is fully borne out by facts. Formerly, 

 Jamaica, like Trinidad at present, w-as dependent for 

 cattle on Venezuela. The food of the animals during 

 their voyage consisted amongst other things of the pulpy 

 legumes of Pithecolobium Sainan. The seeds being very 

 hard were uninjured by the process of mastication and 

 digestion, and they were dejected by the animals in the 

 pastures, where they germinated and grew up into large 

 trees. In this instance the seeds were carried across the 

 sea a distance of about a thousand miles, and there is no 

 doubt that the cattle were directly concerned in their 

 introduction. Indeed, without them the seeds, even if 

 accidentally introduced amongst the fodder, would not 

 have been placed under such circumstances as would 

 have enabled them to give ri-e to plants. In the first 

 place, by being passed through the animals the seeds 

 were softened and the period of germination hastened. 

 In the second place, being embedded in the droppings of 

 the animals the seeds had a suitable medium to protect 

 and promote germination ; and this medium enabled the 

 young plants to withstand the season of drought which 

 is incidental to almost every tropical country. In this 

 instance we have cattle not only the means of introducing 

 the seeds of a valuable tree, but also involuntarily in- 

 strumental in establishing the tree in a new country, and 

 providing shelter, shade, and food for their progeny. 

 Those acquainted with the guango or rain-tree, as this 

 Pithccolobittni is locally called, will fully realize its value 

 as a shade and food-tree for cattle, and they will also 

 appreciate the singular concourse of circumstances by 

 means of which such a tree was introduced to a new 

 country by the very animals which required it most. 



It is possible there may be some who will doubt the pos- 

 sibility of seeds retaining the power of germination after 

 undergoing the processes of mastication and digestion, 

 and especially in the special case of ruminating animals. 

 There is, however, very clear evidence on the subject. 

 It is a common occurrence in India to utilize the services 

 of goats to hasten the germination of the seeds of the 

 common Acacia arabica, known as the babul. This tree 

 belongs to the same natural order as the Pithecolobium, 

 and grows in the poorest and driest soils of India. 

 The babul seeds will not germinate readily in the hot 

 weather, and it is the regular habit, in order to save a 

 season, for a person desirous of a crop of seedlings to 

 make a bargain with a herdsman or a neighbour who 

 possesses a flock of goats to quarter them for some days 

 in a small inclosure in which they are fed on babu 

 leaves and pods. The droppings of the animals contain a 

 certain number of seeds which are uninjured, and these 

 now readily germinate, and give rise to plants the same 



1 "Flora, British West Inli.T Islands," p. 225. 



