3M 



NATURE 



[June 12, 1913 



by Mr. Baker and his colleagues in the Naval Tank. 

 The most noteworthy is that with a series of ship 

 models, each having the same principal dimensions, 

 but with a different distribution of the displacement 

 in a longitudinal direction. The experiments re- 

 vealed the limits of speed to which various forms can 

 be driven without excessive wave-making, and have 

 also increas'ed the general knowledge of eddy-making 

 at the sterns of ships. An extensive series of experi- 

 ments has also been carried out on hydro-aeroplane 

 floats. Fig. 1 gives a general view of the tank with 

 a model in place under the carriage by means of 

 which the model is towed. Fig. 2 shows the wave 

 profiles for a model of mercantile form with fairly 

 bluff ends. It is satisfactory to note how very small 

 the loss of water from the tank still continues — a 

 tribute to its design and construction. 



In the metallurgical department, Dr. Rosenhain 

 and Mr. Archbutt have published the tenth report of 

 the alloys research committee of the Institution of 

 Mechanical Engineers. The report, which deals with 

 the alloys of zinc and aluminium, contains features 

 of great interest in view of the increasing importance 

 of light alloys in aeronautical and instrument work. 

 Dr. Rosenhain and Mr. Ewen have communicated an 

 important paper on intercrystalline cohesion in metals, 

 while Mr. Humfrey has been working on the effects 

 of strain in iron at high temperatures. 



The metrology division has been largely occupied 

 with the arrangements for the reception of the Kew 

 Observatory test work. The behaviour of the silica 

 standard metre has been closely followed, and the 

 value of its expansion-coefficient determined (Mr. 

 Donaldson). 



Dr. Stanton and his staff have carried out extremely 

 valuable work in a number of directions, more par- 

 ticularly on wind-pressures (at the Tower Bridge), on 

 the frictional high-speed flow of water and air in 

 pipes, and on the pressure and flow round aeroplane 

 surfaces. The experiments conducted in the 4-ft. 

 wind channel have afforded valuable information to 

 the Royal Aircraft Factory at Farnborough in design- 

 ing biplanes and dirigible balloons. The Treasury 

 has accordingly authorised the erection of a new 7-ft. 

 channel at the laboratory ; this is now 7 approaching 

 completion. 



The new experimental road constructed for the 

 Road Board is complete, and abrasion and endurance 

 tests have been begun. 



The optical division has been concerned with the 

 testing of photographic shutters, the absorbability of 

 glass for ultra-violet light, and the testing of telescope 

 objectives and trial lenses. The staff took an active 

 part in the organisation and proceeding's of the Optical 

 Convention which was held during the year at South 

 Kensington. 



This short summary may suffice to give a notion of 

 some of the many fields of activity in which the National 

 Physical Laboratorv is working for progress. There 

 are important problems waiting to be taken up ; it is 

 in many cases purely a question of " ways and 

 means " which prevents a start being made. 



THE ROYAL OBSERVATORY, 

 GREENWICH. 



AT the annual visitation of the Royal Observatory 

 *»• on June 7, the Astronomer Royal, Dr. F. W. 

 Dvson, F.R.S., presented his annual report. The fol- 

 lowing extracts indicate the chief items of interest : — 

 The observatorv has ceased to generate its own 

 electric current for lighting and other purposes, and 

 now obtains current from outside. Alternating in- 

 stead of direct current is now used, and a small supply 

 NO. 2276, VOL. 91] 



of direct current is obtained by means of a rotary 

 converter. 



In the new magnetic observatory, shortly to be 

 erected, provision is made for the continuation of the 

 long series of Greenwich observations of the variations 

 of the magnetic elements. This series is unique as 

 regards the length of time during which observations 

 have been made on the same site. The care which 

 has been taken to guard the observatory from all 

 artificial electromagnetic disturbances which could 

 affect the accuracy of the observations has preserved 

 the suitability of the site for such work. 



Observations of double stars have been made with 

 the 28-in. refractor from a working catalogue con- 

 taining all known double stars showing appreciable 

 relative motion, and a number of pairs from the 

 catalogues of Hussey and Aitken under 2" separation. 



k Pegasi was observed on five nights, 5 Equulei on 

 three nights, 70 Ophiuchi on thirteen nights, and 

 e Hydrae on one night. 



The 26-in. refractor, the 30-in. reflector, and the 

 6-in. Cooke triplet have been in constant use during 

 the year. The new cell for the crown lens was 

 received and mounted in July. The adjustment of the 

 crown and flint lenses for tilt and eccentricity relative 

 to one another was made in August. 



During the year 164 plates were taken for deter- 

 mination of stellar parallax, 124 of these being new 7 

 plates and forty being re-exposures of plates taken 

 six months previously. The programme for each star 

 consists of six photographs. Three photographs taken 

 in the evenings are re-exposed in the mornings about 

 six months later, and are then developed. Three 

 plates are exposed in the mornings, and, after re- 

 exposure six months later, are also developed. For 

 several stars the cycle has been completed and the 

 plates have been measured for three stars. The re- 

 sults obtained are + 0-082" ±0017", +0043" +0009", and 

 — 0-014" ±0012". The star which gave a negative 

 parallax is one with a small proper motion. It is 

 considered that these probable errors are too large, 

 and that one of +0005" should be attainable. The 

 increased constancy in the adjustment of the object 

 glass secured by the new cell, and the use of the 

 rotating sector by which the star observed is reduced 

 to the magnitude 10-5111. to ii-ora. of the comparison 

 stars, are expected to make a considerable improve- 

 ment. 



The 6-in. Cooke triplet which belonged to the late 

 Mr. Franklin Adams has been employed in the deter- 

 mination of the photographic magnitudes of the stars 

 brighter than 90m. in the Greenwich astrographic 

 zone. During the year fifty-three photographs of 

 fields compared with the standard polar area have been 

 taken. Fiftv-six plates have been measured, complet- 

 ing the eighty-eight necessary for the whole zone. 

 The catalogue of the resulting magnitudes is nearly 

 completed, and will contain 8000 stars. 



Fifty-nine photographs of Neptune and satellite, 

 taken in 1909-10, have been measured, and the results 

 published. 



At the date of the last report, 152 out of the 206 

 Franklin-Adams photographs had been counted in the 

 manner then explained. During the year fifty of the 

 remaining- plates have been dealt with. The four 

 plates still uncounted have not yet been received from 

 Johannesburg. 



The requisite photometric data for the reduction of 

 these counts to statistics based on actual photographic 

 magnitudes are now being obtained at a steady rate. 

 The plan of taking long exposures on a field and a 

 standard polar area has been abandoned, because of 

 the rarity of nights on which the sky is uniform and 

 constant for more than one hour. Instead of this, 

 exposures of 5m. duration are being taken on the 



