HARDWICKE'S SCIENCE-GOSSIP. 



3t 



the sheet be of such a size as to more than cover the 

 lens-hole of the camera. Now slide this along the 

 tube until it reaches the eye-piece ; it will then make 

 the camera perfectly light-tight. As an extra pre- 

 caution, wrap a space focussing cloth round the 

 whole. Remove the ground glass of the camera and 

 make sure (i) That no light enters the camera 

 except through the eye-hole ; (2) That the eye-hole 

 is exactly in the centre of the lens aperture ; then 

 replace the ground glass screen. 



Screw the substage condenser into the fitting of 

 the microscope, and place lamp behind it, inter- 

 posing a bull's-eye condenser between the lamp-flame 

 and the substage condenser. Focus these condensers 

 and move the lamp, until the object to be photo- 

 graphed is as brilliantly illuminated as possible. 



An inch objective is perhaps the best for general 

 use. Focus the object very carefully on the ground 

 glass screen, altering the focus by means of the 

 microscope coarse and fine adjustments, and not by 

 moving the camera. Examine the image formed 

 under a magnifying lens, and make sure it is as 

 perfect as possible. Then put in the dark slide. 

 With the inch power the exposure is best made by 

 capping the object glass in the same way as is done 

 with the ordinary lens ; in the employment of higher 

 powers exposure must be made by means of the 

 shutter. For the duration of the exposure no cer- 

 tain rule can be given ; much depends on the 

 luminosity of the flame, on the thickness and colour 

 of the object ; but under the inch power one to two 

 minutes is about right. A photometer will be of 

 great service to determine the exact exposure. 



The negative is then developed and the print 

 obtained in the ordinary way ; the pyrogallic acid 

 developer is perhaps preferable for this work to the 

 ferrous oxalate, since it permits greater laxity in the 

 matter of over or under exposure. 



Enclosed I send two half-plate photographs taken 

 in the manner described above ; the one of the head 

 of a female gnat, and the second of a double stained- 

 section of the plane wood ; both of my own 

 mounting. 



I shall be most happy to give any further infor- 

 mation on the subject to any who care to pursue this 

 fascinating union of the camera and microscope. 



A. C. Deane. 

 Wellitigton College, Wokingham. 



A 



ASTRONOMY. 

 By John Browning, F.R.A.S. 

 T the last meeting of the Royal Astronomical 



Society, it was stated that the director of the 

 Lick Observatory had presented to the Society a 

 photograph of the moon more than two feet in 

 diameter, in which the lunar details are very sharply 

 defined. The image of the moon, of which this 



photograph is an enlargement, was taken with the 

 great Lick telescope. 



A paper by Mr. J. Roberts was read on photo- 

 graphs he has taken of the great nebulre in Andro- 

 meda, which he considers afford striking evidence 

 of the truth of Laplace's nebulae hypothesis. Mr. 

 Roberts considers that the small nebulae H 44 and 

 H 55 have both been thrown off by the great nebulae, 

 and may be looked on as planetary nebulae in course 

 of condensation. Mr. Frank McLean read a paper 

 on some photographs of the red end of the solar 

 spectrum from the D to the A line, about one half 

 of the visible spectrum. The photograph is in seven 

 sections, each about fifteen inches long. They were 

 taken with a refractionfgrating having 17,300 lines in 

 the inch, and are the second order of the spectra. 



Messrs. Alvan Clark have undertaken to construct 

 a telescope for the United States Government with 

 an object-glass forty-two inches in diameter. This 

 telescope is to be erected in Southern California, and 

 is expected to be completed in about five years. 



Accounts from San Francisco of the total solar 

 eclipse of January ist, state that it was successfully 

 observed at Brass Valley and many other stations. It 

 would require far more space than is at my disposal 

 to give a brief account of the various observations,, 

 but I may say that Professor Toll took a number of 

 fine photographs of the eclipsed sun, showing the 

 corona extending from ten to twelve degrees. 



Twenty-five negatives were taken at Winnipeg to • 

 measure the brightness of the corona and its sur- 

 roundings. 



At the Lick Observatory successful observations 

 were made, and several photographs were taken. 

 The thermometer fell at different places from seven , 

 to ten degrees during totality. 



There will be no occultation of interest in 

 February. 



At the beginning of February Ursa Major, Lynx, 

 Cancer, and part of Hydra will be on the meridian 

 about midnight. 



Mercury will set on the ist at 6.32 p.m., on the^ 

 15th at 5.13 P.M. 



Venus will be an evening star, setting on the 1st 

 at 9.10 P.M. and on the 28th at 10.8 p.m. 



Mars will be an evening star, setting on the ist at 

 8.4 P.M. and on the 28th at 8. 1 7 p.m. 



Jupiter will rise on the 1st about 5.13 A.M. and! 

 on the 28th at 3.48 a.m. 



Saturn will rise on the ist at 4.58 p.m., and on the 

 3rd he will rise about sunset ; on the 12th he will set 

 about sunrise. 



Earthworms. — Is there more than one British 

 species ? The large ones seem very different from the 

 darker coloured and more cylindrical small wormSj 

 I have seen the latter performing the functions of the 

 adult. They are said to be oviparous, how are the 

 eggs to be found and recognised ?— W. A. Gain. 



