| The basic Clarke Magnetic Electrical Machine was invented
E. M. Clarke (“Magnetician, of 428, Strand, London”) and first described by him in 1836 in the London and Edinburgh Philosophical Magazine. This late version, ca. 1877, is in the apparatus collection of St. Patrick's College in Maynooth, County Kildare, Ireland.
In March 2001 I visited the Garland Collection of Classical Physics apparatus at Vanderbilt University, and there found a Clarke machine in perfect working order. Three views of it are shown below. This instrument is marked "Rhumkorff/À Paris".
||The Clarke Machine at the left is in the Millington/Barnard Collection in the University Museum at the University of Mississippi in Oxford. There is a good proabability that it was bought by Prof. Barnard in the second half of the 1850s. He bought a good deal of French apparatus, but it is not listed in the 1853 Lerebours et Secretan catalogue from which he made many of his purchases. It has the solid driving wheel of the Clarke machines above, but there is no mechanism on the end of the shaft The commutator leaves are held in the two upright brass rods. Was it made by Clarke? Note that a cover, held on by hooks, once covered the rotating coil.|
| Zenobe Theopile Gramme (b.1826) demonstrated his generator
to the Academy of Sciences in Paris in 1871. Unlike the earlier magneto-electric
machines, the Gramme machine used a series of thirty armature coils, placed
inside a revolving ring of soft iron. The coils are connected in series, and
the junction between each pair is connected to a commutator strip on which
two brushes run. The permanent magnets magnetize the soft iron ring, producing
a magnetic field which rotates around through the coils in order as the armature
turns. This induces an EMF in two of the coils on opposite sides of the armature,
which is picked off by the brushes. With thirty coils, the resulting voltage
waveform is practically constant, thus producing a near DC signal.
This type of machine needs only electromagnets to produce the magnetic field to become a true Generator.
The instrument at the right is on display at Birr Castle in County Offaly, Ireland, and is on loan from Trinity College, Dublin.
|| The Gramme machine at the left is in the lecture demonstration
collection at the physics department at the University of Texas at Austin.
It was imported by Queen of Philadelphia and described in the 1888 Queen catalogue as
GRAMME MAGNETO-ELECTRIC MACHINE No. 16. with crank and multiplying gear. All of the experiments pertaining to a course in physics may be shown with this machine, with the exception of voltaic arc light. Two armatures are necessary with it, one of coarse wire for quantity [large currents], and one of fine wire for intensity [high voltages], with some experiments being more successful with the one, and some with the other ... It is equal to about ten cells of Bunsen's Battery, and is very convenient for laboratory use, being easily moved and worked. Price on application."