272 Progress in Physics. [April, 



Mr. Browning has recently published some chromo-lithographs of spectra 

 for the special purpose of keeping records of the position of absorption-bands 

 as observed with his micro-spectroscope. The size of the paper is the same as 

 that of the present journal, and each plate contains seven coloured figures on 

 a black ground, with the places indicated of the principal solar lines ; the 

 memoranda can be made with pencil, or, still better, with a brush, and a 

 tolerable representation of the observed spectrum obtained. This mode of 

 registration will be preferred by many to Mr. Sorby's ingenious notation as 

 adapted to his interference spectrum, an instrument somewhat difficult to 

 procure, on account of the trouble involved in making the plate of quartz of the 

 proper thickness to produce the exact number and position of the bands. 



Dr. Huggins has devised a registering spectroscope, by means of which the 

 positions of lines observed in the spectrum may be instantly registered without 

 removing the eye from the instrument, so as to avoid the loss of time and 

 fatigue to the eye of reading a micrometer-head, or the distraction of the 

 attention and other inconveniences of an illuminated scale. In this instrument 

 the small telescope of the spectroscope is fixed, and at its focus is a pointer which 

 can be brought rapidly upon any part of the spectrum by a screw-head outside 

 the telescope. The spectrum and pointer are viewed by a positive eye-piece 

 which slides in front of the telescope, so that the part of the spectrum under 

 observation can always be brought to the middle of the field of view. The 

 arm carrying the pointer is connected by a lever with a second arm, to the end 

 of which are attached two needles, so that these move over about 2 inches 

 when the pointer is made to traverse the spectrum from the red to the violet. 

 Under the extremity of the arm fitted with the needles is a frame containing a 

 card, firmly held in it by two pins which pierce the card. This frame con- 

 taining the card can be moved forward so as to bring in succession five different 

 portions of the card under the points of the needles ; on each of these portions 

 of the card a spectrum can be registered. The mode of using the instrument 

 is obvious. By means of the screw-head at the side of the telescope, the 

 pointer can be brought into coincidence with a line ; a finger of the other hand 

 is then pressed upon one of the needles at the end of the arm which traverses 

 the card, and the position of the line is instantly recorded by a minute prick on 

 the card. From ten to twelve Fraunhofer lines can be registered in about 

 twelve seconds, and when the same lines are recorded five times in succession 

 on the same card, no sensible difference of position can be detected between 

 the pricks registering the same line in the several spectra. 



A most ingenious application of the spectroscope, and one likely to be of 

 considerable use in many enquiries, has been made by Professor Church. On 

 one side of a crowded court several cases of typhoid fever had been developed. 

 The water used by the inhabitants of these houses was drawn from a rather 

 shallow well, and was highly charged with various unoxidised compounds of 

 nitrogen. It was suspected that the drain from a public urinal might be 

 defective and have allowed egress of its contents into the well. This notion 

 was confirmed by the quantity of common salt contained in the well-water, 

 namely, seven times as much as that in the normal waters of the neighbour- 

 hood. But it received an absolute proof in the following novel manner. Two 

 grammes of a lithium salt were introdued into the urinal. Two hours after- 

 wards lithium was detected spectroscopically in a litre of the well-water before 

 alluded to. A quantity of this water, ten times as large, showed no trace of 

 lithium previously. 



Microscopy. — Dr. Ormerod, of Brighton, uses a new material for grinding 

 sections of bone, tooth, and similar hard tissues. The bone is first cut into 

 slices with a saw in the usual manner, and rubbed down to an even surface on 

 a file or coarse stone; then, using a piece of flat pumice stone as a pad, it is 

 rubbed down with water to the necessary degree of thinness on a piece of coarse 

 ground glass about 6 inches square ; the glasses, when the first roughness is 

 worn off, may be used for giving a still finer surface to the section. Ground 

 glass will be found to act rapidly and efficiently as a grinding agent upon 



