Biografi Jan Ingenhousz

Jan Ingenhousz (8 Desember 1730 – 7 September 1799) adalah ilmuwan Britania Raya kelahiran Belanda yang membuktikan bahwaintensitas cahaya memengaruhi laju fotosintesis pada tumbuhan. Pada tahun 1778, ia mengulangi eksperimen Priestley. Ia menemukan bahwa cahaya matahari berpengaruh pada tumbuhan sehingga dapat "memulihkan" udara yang "rusak".

an Ingenhousz (1730-1799). Dutch-born physician, chemist, and plant physiologist. Showed light is essential to plantrespiration and that the gas plants produce in light is oxygen. He is therefore recognized as the discoverer ofphotosynthesis. 

Jan Ingenhousz was born in 1730 in the city of Breda in what is today the southern Netherlands. At 16, he began his study of medicine at the Catholic University of Louvain, the oldest and most prominent university in Belgium. There he received his MD in 1753. He then studied two additional years at the University of Leiden, where he attended lectures by Pieter van Musschenbroek, an experience that sparked his lifelong interest in electricity. 
 Discovery of photosynthesis 

In the experiment leading to his discovery, he placed plants underwater in a transparent container and saw that the undersides of their leaves made bubbles in sunlight. However, when the same plants were placed in darkness, the bubbles eventually stopped forming. He was also able to see that the leaves and other green (chlorophyll-containing) parts of the plants were the sites where the gas was produced. 
He collected this gas and conducted a series of tests to determine its identity. He eventually found that a smoldering candle would burst into flame when exposed to the unknown gas, which showed it was oxygen (Ingenhousz, 1779, see full citation below). He also found that in darkness plants release carbon dioxide (ibid). In recognition of these discoveries, Ingenhousz was elected to the Royal Society of London that same year. 

Brownian motion

In 1785, Ingenhousz reported that under a microscope he had observed irregular movement of coal dust on the surface of alcohol. He thus described Brownian motion at a much earlier date than did Robert Brown (1827), the English investigator for whom the phenomenon is named. 

Ingenhousz was taken ill during a visit to the Marquis at Bowood in 1799. He died there on September 7th and was buried nearby at Calne.
He collected this gas and conducted a series of tests to determine its identity. He eventually found that a smoldering candle would burst into flame when exposed to the unknown gas, which showed it was oxygen (Ingenhousz, 1779, see full citation below). He also found that in darkness plants release carbon dioxide (ibid). In recognition of these discoveries, Ingenhousz was elected to the Royal Society of London that same year. 
Brownian motion

In 1785, Ingenhousz reported that under a microscope he had observed irregular movement of coal dust on the surface of alcohol. He thus described Brownian motion at a much earlier date than did Robert Brown (1827), the English investigator for whom the phenomenon is named. 

Ingenhousz was taken ill during a visit to the Marquis at Bowood in 1799. He died there on September 7th and was buried nearby at Calne.
Brownian motion 
In 1785, Ingenhousz reported that under a microscope he had observed irregular movement of coal dust on the surface of alcohol. He thus described Brownian motion at a much earlier date than did Robert Brown (1827), the English investigator for whom the phenomenon is named. 

Ingenhousz was taken ill during a visit to the Marquis at Bowood in 1799. He died there on September 7th and was buried nearby at Calne.
In 1785, Ingenhousz reported that under a microscope he had observed irregular movement of coal dust on the surface of alcohol. He thus described Brownian motion at a much earlier date than did Robert Brown (1827), the English investigator for whom the phenomenon is named. 
Ingenhousz was taken ill during a visit to the Marquis at Bowood in 1799. He died there on September 7th and was buried nearby at Calne.
Ingenhousz was taken ill during a visit to the Marquis at Bowood in 1799. He died there on September 7th and was buried nearby at Calne.

The following year, the Austro-Hungarian empress, Maria Theresa read about the success of the English campaign against smallpox and decided to have both herself and her family vaccinated, though her own doctors were against it. She asked the English king, George III, to recommend a suitable physician and, on Pringle's recommendation, Ingenhousz was chosen. He traveled to Austria and successfully vaccinated several members of imperial family, including the empress, which gained him far more fame in his lifetime than did his discovery of photosynthesis. This feat also secured his professional career since he received as a result a pension for life and became body physician to Maria Theresa and her husband Joseph II. Ingenhousz lived the next ten years in Vienna, where in 1775 he married Agatha Maria Jacquin. 

In 1779, Ingenhousz returned to England and traveled to Calne, a small town in southwestern part of the country. There, at Bowood House, the country manor of the Marquis of Lansdowne, in the same laboratory where his colleague Joseph Priestley had discovered oxygen itself only a few years before, Ingenhousz carried out his research on photosynthesis.

Biografi Alexandre Edmond Becquerel

Four successive generations of the Becquerel family were educated at the prestigious French scientific institution of higher learning, the École Polytechnique, and became physics professors at the French Museum of Natural History. Alexandre Edmond Becquerel was the son of Antoine César (1788-1878), discoverer of piezoelectricity, father of Antoine Henri (1852-1908), who discovered radioactivity, and the grandfather of Jean Antoine (1878-1953), who is best known for his work on relativity and the discovery of polarization rotation in the presence of a magnetic field. Though all of these notable scientists carried out a variety of experiments related to optics, it was Alexandre Edmond Becquerel that made the greatest contributions to the field.

Born in Paris on March 24, 1820, Alexandre Edmond Becquerel became first a student, and then an assistant, to his father, and many of his investigations are associated with those of the elder Becquerel. Edmond was, however, particularly intrigued by light and embarked on in-depth studies of the subject. He examined the spectroscopic characteristics and the photochemical effects of the sun, and was especially interested in the phenomena of fluorescence and phosphorescence. To aid in his study of the latter, Becquerel invented the phosphoroscope, a device capable of measuring the duration of time between the exposure of a solid, liquid, or gas to a light source and the substance’s exhibition of phosphorescence. Through the use of the phosphoroscope, the physicist was able to more accurately determine whether or not certain materials exhibited phosphorescence or fluorescence, since one of the key differences between the phenomena is the duration of the excited state lifetime, which is the interval of time that passes before the effect occurs following the absorption of light (fluorescence occurs almost instantaneously after excitation, whereas phosphorescence is characterized by a much longer excited state lifetime). The phosphoroscope also enabled Becquerel to discover phosphorescence in a number of materials that were previously not believed to exhibit the effect.

Alexandre Edmond Becquerel’s work with fluorescence and phosphorescence led him in the late 1850s to develop the idea of utilizing these effects in light sources. He experimentally applied various luminescent materials as coatings to electric discharge tubes, and though he never succeeded in producing a commercial light, his work eventually led to the development of the fluorescent lamps that are widely used in modern times. Findings from many of Becquerel’s studies of luminescence and other areas of optics were published in 1867 and 1868 in the two-volume treatise entitled La Lumiere, ses causes et ses effets. His appointment at the Museum of Natural History occurred in 1878, so that he directly succeeded his well-known father, and he was a member of the Académie des Sciences from 1863 to his death on May 11, 1891

Biografi James Prescott Joule

James Prescott Joule lahir di Salford, Lancashire, Inggris, pada 24 Desember 1818. Dia anak seorang pengusaha bir yang kaya raya, tetapi sedikitpun dia tidak pernah merasakan pendidikan di sekolah hingga usia 17 tahun. Hal ini disebabkan karena sejak kecil dia selalu sakit-sakitan akibat luka di tulang belakangnya. Dia terpaksa hanya tinggal dirumah sepanjang hari. Ayahnya sengaja mendatangkan guru privat ke rumahnya dan meyediakan semua buku yang diperlukan Joule. Tidak hanya itu, ayahnya menyediakan sebuah laboratorium khusus untuk joule.

Joule tidak hanya mengandalkan pelajaran yang dia dapatkan dari guru privatnya. Dia tetap berusaha belajar sendiri sehungga sebagian besar pengetahuan yang dimilikinya diperoleh dengan cara belajar sendiri. Namun, ada satu pelajaran yang cukup sulit dipahaminya, yaitu matematika.

Setelah usia 17 tahun, Joule masuk ke Universitas Manchester denga bimbingan John Dalton, seorang ahli kimia inggris yang terkenal. Joule dikenal sebagai siswa yang rajin belajar, bereksperimen, dan menulis buku. Buku pertamnya terbit pada 1840 daat berusia 22 tahun. Tiga tahun kemudian bukunya mengenai ekuivalen mekanik panas pun terbit. Lalu tahun 1847, dia menerbitkan buku mngenai hubungan kekekalan energi.

Buku-buku karya Joule menarik perhatian Sir William Thomson atau dikenal dengan Lord Kevin. Joule akhirnya bekerja sama dengan Thomson dan menemukan efek Joule-Thomson. Efek tersebut merupakan prinsip yang kemudian dikembangkan dalam pembuatan lemari es. Efek tersebut menyatakan bahwa gas dibiarkan berkembang ranpa melakukan kerja keluar, maka suhu gas itu akan turun.

Joule bersama dua ahli fisika dari Jerman, yaitu Hermann von Helmholtz dan Julius von Mayer juga menemukan hokum kekekalan energi bersama. Hukum ini menyatakan bahwa energi tidak dapat diciptakan atau dimusnahkan, tetapi hanya dapat berubah bentuk menjadi energi listrik, mekanik, atau kalor.

Joule adalah orang yang hobi menggeluti fisika. Dengan percobaan, dia berhasil membuktikan bahwa panas(kalori) tidak lainadalah suatu bentuk energi. Dengan demikian, dia berhasil mematahkan teori kalorik yang menyatakan panas sebagau zat alir. Joule (symbol J) adalah satuan SI untuk energi dengan basis unit kg.m2/s2. nama Joule diambil dari penemunya, James Prescott Joule. Joule disimbolkan dengan huruf J. istilah ini pertama kali diperkenalkan oleh Dr. Mayer of Heilbronn.

Joule diambil dari satuan unit yang didefinisikan sebagai besarnya energi yang dibutuhkan untuk memberi gaya sebesar satu Newton sejauh satu meter. Oleh sebab itu, 1 Joule sama dengan 1 Newton meter (symbol : N.m). selain itu, satu Joule juga adalah energi absolute terkecil yang dibutuhkan (pada permukaan bumi) untuk mengangkat suatu benda seberat satu kilogram setinggi sepuluh sentimeter.

Definisi atau joule lainnya, yaitu pekerjaan yang dibutuhkan untuk memindahkan potensial satu volt atau satu coulomb volt (simbol : C.V).

Ukuran 1 Joule juga dapat didefinisikan sebagai pekerjaan untuk menghasilkan daya satu watt terus-menerus selama satu detik atau satu watt sekon (simbol : W.s). konversi 1 joule adalah sama dengan 10⁷ erg. Ukuran 1 Joule mendekati sama dengan 6.241506363x10¹⁸ eV (electron Volt), 0,239 kal(kalori), atau 2.7778x10^-7 kwh(kilowatt-hour). 2.778x10^-4 wH(watt-houre), atau 9.869x10^-3 liter-atmosfer.

Berkat penemuan-penemuannya, Joule menerima Copley Medal dan menjadi anggota Presiden Asosiasi Kemajuan Ilmu Pengetahuan di Inggris. Meskipun begitu, kedipuannya sangat sederhana. Tidak seperti ayahnya yang kaya raya, Joule hisup miskin dan menghabiskan masa tuanya dalam penyesalan dan kekecewaan karena banyak penemuan ilmiah digunakan untuk berperang.