668 SCIENTIFIC RECORD FOR 1883. 



tion of quartz under the influence of change of temperature, a subject 

 on which much work has already been done, especially by French 

 physicists. 



In the department of electricity attention may be called to a memoir 

 of Hankel (Abhandl. Sachs. Ges. Wissenschaften, xn, 552), which forms a 

 continuation of a line of experiments which he has been following out 

 for a series of years. In this, the sixteenth paper, he gives the thermo- 

 electrical properties of a number of minerals, as helvite, pyromorphite, 

 phenacite, and so on ; his experiments go to show the distribution of the 

 positive and negative electricity on the crystalline surfaces of the min- 

 erals under examination. Routgen has published ( Oberhess. Ges. Natur.- 

 und IleUlcunde, xxn, 40, 97, 181) several memoirs dealing with the elec- 

 trical properties of quartz, and with its optical properties as influenced 

 by electricity. Thus he explains the development of free electricity 

 in quartz by pressure, or by piezoelectricity (as defined by Hankel). 

 This subject has already been treated by J. and P. Curie, but Rontgen 

 carries it further than these authors, making use of a sphere of quartz 

 which could be subjected to pressure in any desired direction. He also 

 explains the development of electricity by change of temperature 

 (thermo-electricity) and by radiation (called actino-electricity). Still 

 further, he shows what changes in the double-refraction of quartz are 

 caused by electrical forces. Kundt ( Wiedemann's Annalen, xviii, 228) 

 has followed a somewhat similar line of investigation, developing the 

 optical behavior of quartz when placed in an electrical field. Thus a 

 prism of quartz, cut parallel to the vertical axis, and with a square sec- 

 tion, was electrified on the opposite pair of prismatic faces with positive 

 and negative electricity. This had the effect of changing the circles 

 of the interference figures, as seen in polarized light, into ellipses whose 

 axes varied in position according to which pair of faces was then elec- 

 trified — the change corresponding to an expansiou or contraction of the 

 crystal. Another memoir by Kundt (Ber. AJc. Berlin, April 5, 1883) 

 is devoted to the explanation of a simple method by which the pyro- 

 electricity and piezo-electricity can be investigated by means of the use 

 of the so-called "Lichteuberg figures." 



The pyro-electricity of sphalerite and boracite forms the subject of an 

 important paper by Friedel and Curie (Bull. Soc. Min. France, vi, 191). 

 The observations on boracite are especially interesting in connection 

 with the results obtained by Mallard, as stated above, that boracite is 

 truly isometric above 205° C. ; they show that boracite becomes pyro- 

 electric only when it ceases, on the fall of temperature, to be isometric. 



The use of the new contact-lever goniometer (Fukl-Hebel Goniometer) 

 of Fuess is discussed by Schmidt (Zeitsch. Kryst., vin, 1). He shows that 

 under favorable circumstances the degree of accuracy is very great. It 

 need hardly be recalled here that the object of this goniometer is to 

 measure the angles between two crystalline faces, which are not capable 

 of affording reflections, so that the reflecting goniometer can be em- 



