596 



NATURE 



[July 8, 1920 



connection with the design of oil-tankers to determine 

 the stresses in the bulkheads of the oil compartments 

 when the ship is pitching. The effect of varying the 

 frequency of the pitch was studied. Thirdly, an 

 apparatus was shown for testing the effects of a 

 screw propeller working behind a ship. If we know 

 the thrust which the screw must develop, and the 

 velocity of the water behind the ship where the screw 

 is working, relative to the velocity of the ship, then 

 the ordinary data can be used to find the dimensions 

 of screw required for a particular service. The object 

 of the experiments is to find out these two factors. 



The heat division of the physics department 

 exhibited, amongst other things, a method of measur- 

 ing humidity based on the property, shown by dry 

 cotton, of absorbing moisture at a very high rate. 

 Two similar coils of cotton-covered wire, one of which 

 is coated with cellulose, are wound on to a single 

 bobbin and connected up to the two sides of a 

 Wheatstone bridge. They are dried by being inserted 

 into a tube containing PoO^, a current being passed 

 through them at th^ same time to ensure complete 

 drying. The coils are then drawn out of the drying 

 tube into the atmosphere the humidity of which is to 

 be measured; the cotton on the uncoated wire 

 absorbs moisture with extreme rapidity, which causes 

 a rise in temperature of the wire, thus upsetting the 

 balance of the bridge and deflecting the galvanometer. 



Another exhibit consisted of a pointolite lamp for 

 calibrating optical pyrometers. The special feature 

 of this instrument is that the tungsten disc had a 

 tungsten-molybdenum couple fused into it, by means of 

 which it was possible to measure the temi>erature of 

 the disc. 



In the optics division of the physics department 

 an apparatus was shown for measuring the coefficient 

 of expansion of short specimens. It has been used 

 lately for determining the coefficient of expansion of 

 various glasses, and has given very interesting results. 

 Interferometer tests and methods of measuring refrac- 

 tive indices were also shown. 



One of the most interesting exhibits in the metro- 

 logy department was a machine which was con- 

 structed to measure accurately to one-millionth of an 

 inch. Slip-gauges are now made accurate to 

 1/100,000 in., and to test them it is advisable 

 to have a machine which can read to one-tenth 

 of this. The machine is used as a comparator, i.e. it 

 measures the difference between the standard gauge 

 and the one under test. The chief feature of the 

 instrument is the complete absence of a micrometer 

 head. The magnification is obtained partly mechani- 

 cally, but mainly by a tilting mirror, which moves 

 the image of a cross wire over a paper scale, giving 

 a magnification such that a movement of J in. over the 

 scale corresponds to a difference in length of 

 1/100,000 in. 



Another machine, for comparing end standards 

 with line standards, can be used for lengths up to a 

 metre. An important point about this instrument is 

 that the two standards under comparison are in the 

 same straight line. 



A new type of micrometer for measuring the 

 diameter of small balls, rollers, etc., was also shown, 

 in which the readings are made on two parallel 

 circles, one of which drives the other through epi- 

 cyclic gearing; tenths and hundredths of an inch are 

 read on one circle, and thousandths, ten-thousandths, 

 and, bv estimation, hundred-thousandths on the 

 other. Both sets of readings are in line with each 

 other, making the instrument very rapid to read. The 

 position of contact is found by means of a small 

 mirror moved bv the tail-stock of the instrument. 



The list of exhibits in the electricity department was 



NO. 2645, VOL. 105] 



large and interesting, but there is only space for 

 reference to a very few of them. A considerable 

 number dealt with photometry. Others were con- 

 cerned with the temperature coefficient of manganin, 

 with the measurement of frequency, efficiency, 

 amplifying power, and characteristics of electric 

 valves, and with a selenium-cell current regulator. 



The Carnegie Foundation and Teachers' 

 Pensions.^ 



npEACHERS' pension controversies are not con- 

 ■■- fined to England. All our recent discussions of 

 this subject have their counterparts in the United 

 States, but there they are immensely complicated by 

 the lack of co-ordination between the different States 

 of the Union. Great diversity exists between the 

 school pension systems which have been adopted or 

 are under consideration, and no attempt seems to be 

 made to bring them into relation one with another. 



The universities and colleges (or such of them as 

 are admitted into association), are the special province 

 of the Carnegie Foundation for the Advancement of 

 Teaching, and the fourteenth report of this body con- 

 tains evidence of work of great value. Beginning in 

 IQ05 with an initial benefaction of ten million dollars, 

 the endowment administered by the trustees has been 

 increased by later gifts and accumulated interest to 

 more than twenty millions. The object of the founder 

 was to provide retiring pensions for teachers in uni- 

 versities, colleges, and technical schools in the United 

 States, Canada, and Newfoundland "without regard 

 to race, sex, creed, or colour"; but the granting of 

 pensions does not h\ any means represent the w-hole 

 of the activities of the trustees. To enable them to 

 discharge effectively the duty laid upon them, they 

 have felt compelled to conduct many inquiries and, 

 when necessary, to offer fearless criticisms, and by 

 these means they have undoubtedlv exercised a power- 

 ful influence on the quality of higher education in 

 America. 



During the year iq 18-19 the trustees disbursed 

 in retiring and widows' allowances a sum of 

 more than eight hundred thousand dollars. But 

 in that vear the old plan of granting such allowances 

 was definitely abandoned in favour of a scheme under 

 which the teacher himself 1s called upon to contribute 

 towards the provision for his own retirement. It is 

 of special interest to observe that, at the time when 

 we in this country were adopting for school-teachers 

 a national pension system on a non-contributory 

 basis, which manv university teachers wish to be 

 extended to themselves, the Carnegie Foundation had 

 come to the conclusion, as a result of thirteen years 

 experience, that a "free pension" could not be a solu- 

 tion of the problem in a democratic country, but that 

 the system must be contractual and rest upon the co- 

 operation of the teacher and his college. This method, 

 in the opinion of the trustees, is the only one that 

 is "just, feasible, and permanent." To this end they 

 organised a Teachers' Insurance and Annuity Asso- 

 ciation, in the control of which the teachers them- 

 selves will have real representation, and invited the 

 universities and colleges to adopt pension schemes 

 based on joint contributions by the teacher and his 

 institution and worked by means of policies issued 

 bv the new association. The trustees continue the 

 system of free pensions for those who were in the 

 service of associated institutions before a certain date, 

 but for others will content themselves with the pro- 



1 Carnegie Foundation for the Advancement of Teaching, Fourteenth 

 Annual Report of the Chairman and of the Treasurer. (New York, 1919-) 



