:88 



NATURE 



[July 12, 1917 



temperature. At a height of 25 ft. is the floor 

 which supports the driving- clock and other parts 

 of the mechanism, and on this floor also is a room 

 designed for silvering the large mirror. Near the 

 centre of the pier there is an opening, 14 ft. in 

 diameter, which accommodates an electric elevator 

 for handling the mirror. 



On the south side of the pier is an extension, 

 with a slope equal to the latitude, designed to 

 carry large spectrographs when the instrument is 



Fig. 



-The 150-ft. tower telescope, taken from the summit of 

 the 60-ft. tower telescope. 



used in coude form. It is large enough to permit 

 th€ use of a concave grating of 21 ft. radius, or 

 a plane-grating spectrograph of 30 ft. focal 

 length, the light being received through an aper- 

 ture in the lower portion of the polar axis. 



The foundations for the building consist of forty 

 concrete piers, each 6 ft. square at the base and 

 6 ft. high, arranged in two concentric rings. 

 The sides consist of a steel framework, with an 

 inner covering of sheet metal. The dome (Fig. 3) 



NO. 2489, VOL. 99] 



is 100 ft. in diameter, and is double-sheathed for 

 protection of the telescope against great changes 

 of temperature. An unusual permanent feature 

 of the dome is a ten-ton travelling crane, which 

 has also been utilised in the work of erection. The 

 movements of the dome and telescope involve the 

 use of no fewer than thirty-five electric motors, 

 and the wiring proved to be a task of very con- 

 siderable difficulty. 



This brief account may suffice to give some 

 conception of the immense amount of technical 

 skill and foresight which has been called for in 

 the design, construction, and housing of the new 

 telescope. That the enterprise may be rewarded 

 by a rich harvest of new discoveries will be the 

 earnest hope of all who are interested in the 

 progress of science. 



Fig. 4 is from a recent photograph of the 150-ft. 

 tower telescope of the Mt. Wilson observatory. 

 In this instrument a beam of sunlight is reflected 

 in a vertical direction by a coelostat situated within 

 the dome, and an image of the sun is formed at 

 the base of the tower by an object glass near the 

 summit. The special advantage of this arrange- 

 ment arises from the fact that the greater part of 

 the optical path is removed from the disturbing 

 atmospheric conditions which are usually present 

 at the ground level. The 75-ft. spectrograph, and 

 other appliances used wdth the telescope, are con- 

 tained in a deep pit beneath the tower, and 

 constant temperature is easily maintained under 

 these conditions. An important feature of the 

 construction of the tower is that there is an inner 

 framework which supports the optical parts, and 

 an outer casing designed to protect the inner tower 

 from disturbances by wind. 



MATERNAL AND CHILD WELFARES 



THE two handsome volumes before us, pub- 

 lished under the auspices of the Carnegie 

 United Kingdom Trust, are the most recent proof 

 of the rapidly increasing attention and importance 

 attaching to the subject of maternity and child 

 welfare. The need for attention to the conditions 

 of birth and the rearing of children has impressed 

 itself upon the public in large measure in conse- 

 quence of two considerations, the steady and 

 persistent fall in the national birth-rate and the 

 terrible loss of the most virile part of our popu- 

 lation in the present great world-war. 



T^e first volume, by Dr. Hope, the well-known 

 medical officer of health of Liverpool, gives a 

 general outline of the subject. In fifty-six pages 

 he sketches the chief causes of maternal and 

 infant mortality, the facts as to its national and 

 local incidence, and the various organisations for 

 the care of mothers and infants. Ante-natal care 

 is considered, and the importance of further atten- 

 tion to the prevention of still-births is emphasised. 

 The care of mothers during the lying-in period 

 and after it, and the general subject of infant 



1 Report on the Physical Welfare of Mothers and Children. England 

 and Wales. Vol. i., pp. xvi+4;4. By Dr. E. W. Hope. Vol. ii., pp- 

 viii + 190. By Dr. Janet M. Campbell. (Ibe Carnegie United Kingdom 

 Trust, 1917.) 



