Dee. 2i, 18S8.J 



SCIENTIFIC NEWS. 



629 



Correlation, (2) Simplicity, (3) Comprehensiveness, (4) 

 Naturalness, and (5) Convenience. 



In a properly Correlated system all the quantities con- 

 sidered should be so connected by the equations repre- 

 senting the laws of nature, that no co-efficients are 

 required in expressing any unit in terms of others, for 

 Simplicity, quantities essentially the same should be 

 measured by the same units, and to be Comprehensive, 

 the system should embrace all the physical ideas which 

 occur ; to be Natural its units should be closely or 

 decimally connected with natural units, and for Con- 

 venience, they should agree with established (though 

 arbitrary) units, either actually or decimally. In the two 

 systems referred to, correlation has been more completely 

 realised than any of the others, but simplicity is by no 

 means satisfactory, and the want of comprehensiveness 

 was discussed by Professor Rucker at the last meeting. 

 The " second " is unnatural in not being a decimal sub- 

 division of the solar day, and the gramme is derived from 

 the centimetre by assuming the density of water to be 

 unity, whilst the inconvenience arising from the relation 

 between the horse-power and the watt or the erg, is 

 universally acknowledged. 



Two gsneral formula? are given in this paper for con- 

 verting magnitudes expressed in Practical, and C. G. S. 

 electro-magnetic measure into C. G. S. Electrostatic units. 



Though the formula? may be found useful, the author 

 thinks it would be far better to adopt one system for all 

 measurements, and suggests a " Coalition System," in 

 which v is taken as the unit velocity. If in this 

 system the " second " be retained, then ihe unit of length 

 will be 30 earth-quadrants, and if the quadrant be taken 

 (as in the present practical system) as the unit of length, 

 then the unit of time will be ~ sec. The influence of 

 such changes on present standards is then discussed, and 

 the relation between the new unit of power and the 

 horse-power found to be unsatisfactory. 



To endeavour to bring the horse-power and the unit 

 of power into decimal relation, the author expresses the 

 physical quantities in terms of length, time, and power, 

 from a table of which it is evident, what units will be 

 affected by changing the unit of power, and tables of 

 converting factors are given when the latter unit is taken 

 as '746 watt or as 7^46 watts. 



A summary is given towards the end of the paper in 

 which the union of the two electrical systems by choosing 

 w sec. as the unit of time is recommended, the effect of 

 which is to make the unit of capacity -g J ff Farad., and 

 that of resistance 30 ohms. Before concluding, the author 

 deprecates the practice of giving specific names to par- 

 ticular units, for by so doing subsequent necessary 

 changes are made much more difficult. 



Dr. S. P. Thompson thanked the author for his prefix, 

 megisto, denoting multiply x 10". Referring to the 

 choice of air as the standard for specific heat, he remarked 

 that convenient coincidences were not always to be 

 trusted, and that the specific heat of air depended on 

 the pressure to which it was subjected. 



Some Improved Polarising Apparatus for microscopes 

 were exhibited and described by Dr. S. P. Thompson. 

 For polariser, he uses an Ahrens prism, and for analyser 

 a flat-ended one of his own design. The Ahrens prism 

 is formed from a rectangular block of spar, two faces of 

 which are perpendicular to the optic axis ; two cuts 

 parallel to the axis are made from the middle of one side 

 to the ends of the opposite, and the cut faces are polished 

 and cemented by Canada balsam. A short prism with 



wide angle is thus obtained which can be readily fitted 

 to the substage of the microscope. The analyser, which 

 consists of two wedges of spar, is mounted in a tube 

 which fits on the eyepiece, and by recognizing that the 

 upper end need not be larger than the pupil of the eye, 

 the author has been able to considerably reduce the 

 length of the prism, and still keep the bottom end large 

 enough to collect all the rays passing through the eye 

 piece. 



Several ingenious methods of cutting spar so as to 

 produce prisms with minimum waste, were described 

 and illustrated by models, and a " nicol" made by the 

 inventor at the age of seventy-nine was exhibited. 



Mr. Lant Carpenter asked the author why he con- 

 demned analysers placed directly behind the objective, 

 for in his experience this arrangement gave the most 

 satisfactory results. 



In replying, Dr. Thompson said his experience was 

 decidedly different from that of Mr. Lant Carpenter, and 

 mentioned that Zeiss had abandoned the common arrange- 

 ment and now introduced his analysers between the two 

 lenses of his Huyghenian eye-pieces. 



ZOOLOGICAL SOCIETY. 

 At the meeting held on December 4th, Professor 

 Flower, C.B., LL.D., F.R.S., President, in the chair, 

 Mr. Oldfield Thomas, F.Z.S., gave an account of the 

 Mammals obtained by Mr. C. M. Woodford during his 

 second expedition to the Solomon Islands. The author 

 s'ated that the total number of species of mammals 

 known from the Solomons was brought up by the 

 present collection from thirteen to twenty-two, and that 

 of these no less than eight had been discovered by Mr. 

 Woodford, his previous collection having contained ex- 

 amples of two and the present of six new species 

 There were also two new genera of bats to be added to 

 the one previously described. Mr. F. E. Beddard read 

 a paper upon the genus Clitellio, which had been re- 

 cently investigated by him at the Marine Biological 

 Station at Plymouth. The paper contained an account 

 of the anatomy of two species, Clitellio arenarius and 

 C. ater ; the most important fact referred to was the 

 presence of an oviduct, which had only lately been 

 found in the Tubificidas (in the genus Psammoryctis). 

 The paper also contained some remarks upon the 

 synonymy of the two species, particularly of C. ater, 

 which was probably identical with d'Udekem's Tubifex 

 benedii and with Zeuger's Peloryctis inqiulina. It was 

 also pointed out that C. ater is not congeneric with 

 C. arenarius, but probably belongs to Eisen's genus 

 Hemitubifex. Professor Howes and Mr. Davies read a 

 paper on the distribution and morphology of the super- 

 numerary phalanges in the Anurous Batrachians. The 

 authors described for the first time the primary mode ot 

 development of a supernumery phalanx. They con- 

 cluded that the same is in the Anura identical with the 

 interphalangeal syndesmoses, and that the syndesmoses 

 and phalanges are derivatives of a common blastema. 

 In its fully differentiated condition the structure in 

 question was shown to be functional in receiving the 

 direct thrust under the weight of the falling body in 

 saltation; all the variations in structure being readily 

 intelligible on that view. 



The authors discussed the bearings of the facts upon 

 classification and upon the broader question of the mor- 

 phology of supernumerary phalanges in general. They 



