128 ANNUAL OF SCIENTIFIC DISCOVERY. 



the dimensions of the inductive surfaces, in the apparatus referred to, being 

 nine inches in diameter, and nine inches apart. The inductive surface men- 

 tioned is also a plane. A ball cannot properly be used for this purpose; for 

 the lines of inductive force originating at it cannot then be perpendicular to 

 the layer of gold-leaf forming the coating of the sulphur. The consequence 

 would be, that this layer of gold, being virtually extended along the lines of 

 inductive force, i. e., having parts nearer to, and parts more distant from 

 the inductric, will be polarized according to well-known electrical actions, 

 will have opposite states at those parts, will show these states by a carrier, 

 and will give results not belonging merely to insulating particles in a section 

 across the lines, but chiefly to united conducting particles in a section oblique 

 to or along the lines. The carrier itself must be perfectly insulated the 

 whole time, or else a case of induction, not including the sulphur, and en- 

 tirely different to that set out with, is established. It must not even extend 

 by elongation into parts of the field of induction where the force differs in 

 degree, or else errors of the same kind as those described with the ball in- 

 ductric will occur. It should also be so used as to receive no charge by 

 convection. When introduced between the inductric and the sulphur, it is 

 very apt, if the charge be high, or if particles adhere to the inductric, to 

 receive a charge. This is easily tested by introducing the earner into its 

 place, abstaining from touching the gold-leaf, withdrawing the carrier, and 

 examining it; it is not until this can be done without bringing away any 

 charge, that the carrier should be employed to touch the gold-leaf surface, 

 and bring away the indication of its electrical state. As before said, if, when 

 the state of matters is perfect, and no convection interferes, the gilt sulphur 

 be put into its place, left there for a short time, and brought away again, it 

 will be found without any charge either of the gold-leaf coating or the sul- 

 phur. If it be put into place, the coating next the inductric be uninsulated 

 for a moment only, and the plate brought away, that coating will then 

 appear positive. If it be put into place, and the further gold-leaf be uninsu- 

 lated for a moment, that coating, when the plate is brought away, will be 

 found negative. These are all well-known results, and will always appear, if 

 convection and other sources of error be avoided. 



ELECTRIC APPARATUS AND EMBRYOLOGY OF THE SKATE. 



At a recent meeting of the Boston Society of Natural History, Dr. Jeffries 

 Wyman stated that he had recently examined the electric apparatus in the 

 tail of one of our common skates (Raia Icevis). The electric organs have 

 been noticed by several anatomists, but have been fully described in Raia 

 latis and other species, by Robin. In the species dissected b}- Dr. Wyman, 

 the organs were more largely developed, extended further up into the base 

 of the tail, and were more uncovered by the muscles, posteriorly, than in 

 the ones examined by Robin. Thus far, no positive proof has been adduced 

 to show that the organs in question really constitute an electric apparatus. 

 Structurally they resemble those of the Torpedo and Gymnotus, but have 

 not been observed to evolve electricity, though it has been stated that if a 

 living skate is held by the tail, an electric shock is felt. 



Dr. Wyman also stated that he had seen the horny shell of the egg of the 

 skate In the process of formation. He had found one in each oviduct, sur- 

 rounded by the glandular enlargement which is visible near its middle. 

 That portion of the duct was very much thickened, and mainly consisted of 



