The 9th Massachusetts Artillery was also known as Bigelow’s Battery. During the battle of Gettysburg, it served as a member of McGilvery’s Brigade in the Artillery Reserve, Army of the Potomac. The unit was commanded by Captain John Bigelow (1841-1917). The unit has 110 men engaed at Gettysburg using 6 Napoleons with 8 killed, 18 wounded and 2 who went missing.
John was a senior at Harvard when he enlisted in the Army. He served valiantly during the Civil War advancing from First Lieutenant to Brevet Major in 2nd Battery, Light Artillery, MA Vols., and 9th Battery, Light Artillery, MA Vols. He was badly wounded at the battle of Malvern Hill on 01 July 1862 and at Gettysburg 02 July 1863. John was a machinery designer and "inventor" by trade, and lived in Philadelphia, PA then Minneapolis, MN. He and Julia (Barber) had no children. SOURCE
The 9th Massachusetts Battery Monument is located on Wheatfield Road. If entering off of Route 15/Emmitsburg Road, the monument is .26 miles on the left or north side if traveling east along the road. The Peachfield is also just to the west of this position. 
Parking is available at small, cutout shoulders along the road, some wide, some narrow. Be sure to stay off the grass or you will be tickete by park police. I visited this monument on Thursday, July 5, 2012 at 12:38 P.M. I was at an elevation of 570 feet, ASL. I used a Canon PowerShot 14.1 Megapixel, SX210 IS digital camera for the photos.
The Draw the Sword site helped out by the NPS narrative and the SIRIS site offers the following description: he monument cost $1,000.00. Rough-hewn monolith contains various relief elements in a recessed area on the front and a long plaque with text describing the events of July 2, 1863 on the rear. Decorative elements include a palm frond and the State Seal. Monument is a 3.10×3.1 foot granite monolith with bronze inscription tablet on the north side and dedicatory inscriptions, and a relief and coat of arms on the south face. Overall height is 8.5 feet. It indicates the first position held by the 9th Massachusetts Battery on July 2, 1863, before being forced to withdraw in the face of the assault by Barksdale’s Confederates. Marks position held by Bigelow’s Battery when they shelled Confederates at Rose Farm pm of July 2, 1863.
The monument was erected on July 2, 1885 by the Commonwealth of Massachusetts. The monument is of Quincy granite with a bronze plaque on the reverse side. Overall the monument is approximately 9 feet X 4 feet 1 inch X 3.5 feet 5 inches. The monument was sculpted by John Bigelow and Charles Reed and fabricated by the Boston Marble and Granite Company. Interestingly enough, this unit was commanded by a Captain John Bigelow. I wonder if the two are the same person. If so this would be the first instance of a commander sculpting his unit's own monument. There is an inscription incised on the front granite and another inscription on the reverse side bronze plaque, all of which read:
(Front):Ninth Mass.
Battery
Captain Bigelow
July 2, 1863.
Killed - Wounded
2 Officers 1
3 Non-Comm Officers 6
5 Enlisted Men 13
10 Total 20
80 Horses
(Back):9th Massachusetts Battery
Capt. John Bigelow
1st Position left gun Wheatfield Road
4.30 to 6 p.m. July 2, 1863
Shelled Confederate batteries on Emmitsburg Road also the enemy around Rose Farm Buildings. Enfiladed with canister Kershaw's Brigade C.S.A. moving across field in front from Emmitsburg Road to woods on left where battle was raging in front of Round Tops
6 p.m. alone in field Graham's Brigade 3d. Corps forced from Peach Orchard had retired by detachments
By "Prolonge Firing" retired before Kershaw's Skirmishers and Barksdale's Brigade C.S.A. 400 yards.
2d position angel of stone wall near Trstle's House where the battery was halted by Lieut.-Colonel McGilvery and ordered to hold enemy in check until line of artillery could be formed 560 yards in rear was without support and hemmed in by stone wall enemy closed in on flanks men and horses were shot down when finally overcome at 6.30 p.m. Lieut.- Colonel McGilvery had batteries unsupported in position near the Weikert House covering opening in lines between Round Tops and left of 2d Corps 3/4 mile occasioned by withdrawal of Graham's Brigade
7.15 p.m. Willard's Brigade 2d. Corps and later Lockwood's Brigade 12th. Corps came to support of artillery
8 p.m. the enemy finally repulsed
The 9th Massachusetts Battery Monument is a contributing feature to the Gettysburg National Military Park Historic District which is nationally significant under NR Criteria A, B, C & D. Areas of Significance: Military, Politics/Government, Landscape Architecture, Conservation, Archeology-Historic. Period of Significance: 1863-1938. The original National Register Nomination was approved by the Keeper March 19, 1975. An update to this nomination was approved by the Keeper on January 23, 2004. The monument is identified as structure number MN169-B.
From the Nomination Form:
1 of 25 mns in Park honoring State's commands in Gettysburg Campaign. Marks position held by Bigelow's Battery when they shelled Confederates at Rose Farm pm of July 2, 1863. Located on N side of Wheatfield Rd about mid-way between 2 Sickles Aves.
Short Physical Description:
MN & 2 cannons. Granite monolith, 3'10"x3'1", 8'5" high. Bronze inscription tablet on N side. Dedicatory inscriptions, reliefs and coat of arms on S side. MN flanked on E/W sides by bronze Napoleon cannon on cast-iron carriages.
Long Physical Description:
Monument that has two flanking bronze Napoleon cannons. Monument is a 3.10x3.1 foot granite monolith with bronze inscription tablet on the north side and dedicatory inscriptions, and a relief and coat of arms on the south face. Overall height is 8.5 feet. Cannon flank the monument on the east and west sides mounted on cast iron carriages. Located on the north side of Wheatfield Road about mid-way between the two Sickles Avenues.
My Sources
1.
NRHP Nomination Form
2.
SIRIS
3.
Stone Sentinels
4.
Virtual Gettysburg
5.
Draw the Sword
6.
Historical Marker Database
7.
9th Massachusetts Artillery